WMU-Cooley Grad: Article Published in the Florida Defender

Exclusion of Partial DNA Specimens, Specimens from Multiple Contributors and the Lab-Created Phenomenon of Allelic Dropout by Jason S. Downs

Jason S. DownsWMU-Cooley graduate Jason S. Downs is an attorney in Brevard County at Murphy’s Law Offices, P.A. His article, Exclusion of Partial DNA Specimens, Specimens from Multiple Contributors and the Lab-Created Phenomenon of Allelic Dropout, published in the Winter 2019 issue, Volume 31, No. 4, of the Florida Defender, A Publication of the Florida Association of Criminal Defense Lawyers. Downs is a member of FACDL and the Young Lawyers Division of The Florida Bar. Before law school, he was a successful independent analyst and brief author. He was retained by many Florida criminal defense attorneys to lend his skills in formulating winning defense strategies and developing theory. He has authored hundreds of successful dispositive motions and is the author of dozens of prevailing appeals in all levels of the Florida court system and in the Supreme Court of the United States.

On a typical September evening

In a beach community of Florida, multiple men invaded the home of a local drug dealer.

The result was an executionstyle murder. Some co-defendants were quick to confess after having lost their stomach for the reality of the situation. Their recitation of facts differed and the prosecution ultimately came down to reliance on several DNA specimens. Of those specimens, the only clear donor was the victim. All other DNA evidence included partial specimens and specimens from multiple contributors. All allegedly involved were convicted, one of which was only prosecuted because his DNA allegedly appeared as part of a partial specimen and a specimen coming from multiple contributors. Of critical importance was a blood sample located under a fingernail of the victim. That specimen contained DNA from multiple contributors. The victim was a 13 of 13 allelic match for one specimen. A co-defendant was identified as a 13 of 13 allelic match and proven to be another contributor. However, the defendant in question, “k,” was found to be a 2 of 13 allelic match as the third contributor and was prosecuted under this “scientific” analysis nonetheless.

All too often our courts are presented with circumstances where multiple contributors donate genetic material to a crime scene, and all too often our crime labs are presented with an overlap between those multiple contributors and the remaining, non-overlapping portions of the specimens, don’t match either contributor.

As the practice of DNA prosecution and defense continues to evolve with the advancements in technology, we as members of the legal community owe a duty to society at large to continue to stay with the scientific curve. There are ever-changing discoveries coming to light which seem to turn our legal theories regarding DNA on their heads. Even as this article is written, there are undoubtedly further advancements being made. The Innocence Project has documented no less than 350 men and women who have been wrongfully convicted, only to have their convictions overturned as DNA technology has continued to advance.

At present, there are two issues which are consistently overlooked in the legal community, all while the scientific community has been screaming “look at this!” First, partial DNA specimens or DNA specimens originating from multiple contributors are not sufficient to be submitted as evidence according to the Federal Rules of Evidence. Second, the so-called phenomenon of “allelic dropout” cannot be used as a means to exclude a subject as a potential contributor. Such evidence is contradictory to the standards set forth in both Frye and Daubert and is nothing more than a prejudicial misdirection intended to lead a jury astray.

Partial DNA Specimens Originating from Multiple Contributors Should be Excluded as a Matter of Law:

“Expert” Testimony is too Unreliable Given the Width of Differing Scientific Opinions and Evidentiary Standard.

The fact of the matter is the “evidence” and the expert testimony go hand-in-hand. Such complicated scientific evidence requires the testimony of an expert. In any case, a crime lab analyst will seek to explain the state’s lack of conclusive findings to include the accused as a contributor. They will do so by using unreliable principles and methods. The analyst will seek to use those unreliable standards to support the use of a partial DNA specimen originating from multiple contributors and this very practice does not satisfy the second or third prongs of Fed. R. Evid. 702 because the opinion offered in support of such evidence is flawed at its conception. Basing testimony on scientific practices that are not generally accepted in the scientific community fails to stand up to Fed. R. Evid. 702, and therefore the evidence that the testimony seeks to support must also be excluded.

The most reliable scientific methods for collection and analysis of DNA evidence, as well as what would be considered “generally accepted” under Frye and meeting the “scientific knowledge edge” standard of Daubert, must be modeled after the FBI’s own standards. The FBI recommends crime scene samples be taken from a single source, not multiple sources. The reason the FBI makes this recommendation is because when more than two alleles at a locus are used for searching, the number of partial matches from unrelated individuals increases very quickly.

The FBI goes on to state that when partial DNA matches occur as the result of a moderate stringency search [a search that requires all alleles to match] of an offender database, attempts to evaluate the significance of that partial match have complications. The first such complication is when many comparisons have been made; there will be partial matches between unrelated profiles, and the number of these increases with the size of the database. Experts explain the difficulties in interpreting specimens containing more than one contributor by stating,

“By their very nature mixtures are difficult to interpret. The number of contributors is often unclear. Although the presence of three or more alleles at any locus signals the presence of more than one contributor, it often is difficult to tell whether the sample originated from two, three, or even more individuals because the various contributors may share many alleles. If alleles 14, 15 and 18 are observed at a locus, they could be from two individuals, A and B, where A contributed 15 and B contributed 14, 18. Alternatively, A could have contributed 14, 15 while B contributed 15, 18, and so on. There might also be three contributors. For example, A could have contributed 14, 15, while B contributed 15, 18 and C contributed 15. Many other combinations are also consistent with the findings. A study of one database of 649 individuals found over 5 million three-way combinations of individuals that would have shown four or fewer alleles across all 13 commonly tested STR loci.” [Emphasis added].

When this issue arises at trial, the state argues the accused “cannot be excluded” as a possible contributor because of a two-way match, as the state did in the case described herein.

Calling such a specimen a “match,” which is in fact, nothing close to a “match,”

Is nothing short of misleading and prejudicial.

The Scientific Working Group on DNA Analysis Methods (SWGDAM) works under the supervision of the FBI, the FBI follows the guidelines set forth, and the recommendations made, by SWGDAM. According to SWGDAM Interpretation Guideline 4.1: “The laboratory must perform statistical analysis in support of any inclusion that is determined to be relevant in the context of a case, irrespective of the number of alleles detected and the quantitative value of the statistical analysis.” In criminal prosecutions, the state will not offer such statistical analysis to explain the reason behind their decision to not exclude the accused as a possible contributor to the mixture of DNA. Buckleton and Curran (2008), experts in the field of DNA Human Identification, cited at the Symposium, at FN 8, advise, “There is a considerable aura to DNA Evidence.

Because of this aura, it is vital that weak evidence is correctly represented as weak or not presented at all.” [Emphasis added]. States commonly fail to adhere to this expert advice. The state witnesses never discuss why the suspect must be included as a contributor — they only argue as to why the accused cannot be excluded. Also bear in mind that the state will send the accused’s DNA sample to the crime lab and ask them specifically to see if the accused is a “match.” How many millions of individuals would not have been excluded based on the same mixture of DNA? The Symposium advises “when determining the number of contributors, the technicians must make assumptions,” [emphasis added] and Curren and Buckleton go on to advise, “The risk of producing apparently strong evidence against an innocent suspect by this approach was not negligible.” Here, the crime lab assumptions about whether Δ could possibly be a match for the partial mixture of DNA located at the scene of the crime, but they failed to include the statistical analysis required by the SWGDAM guidelines (which is the FBI standard) which would illustrate just how many individuals in the world could possibly be contributors to the same DNA mixture. To further illustrate the danger in inferring possible inclusion, the Symposium lists what it considers “issues” with complex mixtures. Of these issues, two are applicable here: “Increased likelihood of falsely including a non-contributor,” and “Increased likelihood of being inclusive.”

Simply stated, in this case, as in many involving DNA evidence, the laboratory technicians cannot find a match to the crime scene contributor of the DNA. Rather than excluding any of the major suspects suggested by the state, the “crime lab” arm of law enforcement sees if they can “squeeze” the suspect into the DNA puzzle. This is what renowned DNA expert William C. Thompson calls “painting the target around the arrow.” He says when there is only a partial match derived from mixed samples of DNA, the technician says, “To heck with the analytical and stochastic thresholds [the value above which it is reasonable to assume that allelic dropout has not occurred within a single-source sample], I am just going to see if the suspect profile(s) can fit into the mixture allele pattern observed — and then if an allele is not present in the evidentiary sample try to explain it with possible allele dropout due to stochastic effects.” SWGDAM and the FBI remind crime labs that “The application of a stochastic threshold to the interpretation of mixtures should take into account the additive effects of potential allele sharing.” “Without statistical measures, statements such as “cannot exclude” do not comply with the 2010 SWGDAM guidelines, but are still being used by some crime labs.” [Emphasis added].

Based on expert opinion and the policies of FBI Laboratory Services, any testimony or evidence in support of the use of less than a 13 of 13 allelic match from a mixture of DNA from multiple contributors would not be based on sufficient facts or data to satisfy Fed. R. Evid. 702 (b); nor would the testimony be the product of principles and methods reliable enough to satisfy Fed. R. Evid. 702 (c). Further, the most prominent experts in the field do not recognize the use a of partial DNA profile in the case of multiple contributors, and laboratory findings such as “cannot exclude,” as well as inclusion based on minimal partial matches without statistical analysis, are not “generally accepted” scientific methods, as defined by Frye. The high probability of individuals — whether related to the crime or not, and whether related to the accused or not — being a partial match to the crime scene evidence is overwhelming. In conclusion, a partial allelic match originating from a specimen containing DNA of multiple contributors does not satisfy the second and third prongs of Fed. R. Evid. 702, nor does it satisfy the “generally accepted” rule of Frye or the “scientific knowledge” standard of Daubert and should be excluded as a matter of law.

The So-Called Phenomenon of Allelic Dropout

Cannot Be Used as a Means to Not Exclude a Subject as a Potential Contributor.

The FBI defines allelic dropout as the failure to detect an allele within a sample or failure to amplify an allele during PCR. Simply stated, if the laboratory technician believes the allele should be present but fails to detect the allele, the technician simply infers that the allele was present, but has “dropped out” or disappeared. That unfounded, discredited notion of allelic dropout, if analogized in even simpler terms, could rationalize absurd inferences of other sorts. Imagine the police assuming a murder weapon was present, simply because they believe it should be there, but they failed to locate it.

Sufficient data now exists to discredit the so-called phenomenon of allelic dropout. The argument should be made that allelic dropout evidence is precluded by Fed. R. Evid. 702 and Frye’s “general acceptance” doctrine and the “scientific knowledge” standard of Daubert as being insufficient and unreliable; and is therefore inadmissible as being more prejudicial than probative. So-called allelic dropout is not a sufficient scientific explanation for an utter lack of evidence, and is not an excuse for the crime labs to testify that a subject “cannot be excluded” as a possible contributor. While the states may suggest a partial allelic match (such as the 2 of 13 allelic match in the case above) is evidence sufficient to include a subject as a possible contributor to the crime scene evidence, the FBI states — in scientific terms — the potential allelic dropout of the remaining alleles “raises the possibility of contributors having genotypes not encompassed by the interpreted alleles [meaning, in lay terms, there is an endless number of possible contributors], and such data should not be used to support an inclusion.” Based on the FBI’s own recommendations, such data should not be used to allow a crime lab analyst to state that the accused “cannot be excluded.”

Such partial DNA evidence originating from multiple contributors simply must be excluded unless there is complete and conclusive evidence of a DNA profile, based on all 13 alleles being present, and in accordance with the FBI’s guidelines. Allowing an analyst to testify that the accused “cannot be excluded” is no different, given the powerful impact DNA evidence can have upon a jury. It is misleading and far more prejudicial than probative. Once the proverbial bell has been rung, it cannot be un-rung. This is what the state legislatures intended to protect against when they adopted and codified portions of the Fed. R. Evid. For instance, Florida law states, “Relevant evidence is inadmissible if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of issues, misleading the jury, or needless presentation of cumulative evidence….”

Florida courts were quick to act and made holdings excluding evidence where the probative value of the evidence was substantially outweighed by the danger of unfair prejudice and was misleading to the jury, and by holding that the trial court is obligated to exclude evidence where unfair prejudice outweighs the probative value in order to avoid the danger that a jury will convict a defendant based upon reasons other than evidence establishing his/her guilt. By failing to follow the “generally accepted” methods of the scientific community which demand the accused be excluded as a possible contributor, the states continue to ignore their own evidentiary rules and those of the federal government. By doing so, they impose an extraordinarily fatal prejudice that could not be overcome if presented to a jury.

In accordance with the intent of Fla. Stat. §90.403, the Federal Rules, and the corresponding rules of most states, the phrase “cannot exclude” is a matter of admissibility, not weight, and must be excluded by trial courts. By testifying that the accused cannot be excluded, the crime lab analysts attempt to create an aura of scientific validity, based on wholly unscientific methods, which are actually nothing more than inferences from technicians who happen to be an arm of law enforcement.

In some instances, an STR test will detect only one of the two alleles from a particular contributor at a particular locus. Generally, this occurs when the quantity of DNA is relatively low, either because the sample is limited or because the DNA it contains is degraded, and hence the test is near its threshold of sensitivity. The potential for allelic dropout complicates the process of interpretation because analysts must decide whether a mismatch between two profiles reflects a true genetic difference or simply the failure of the test to detect all of the alleles in one of the samples. The FBI even requires the forensic index to be searched at moderate stringency when targeting partial matches against familial searches. Moderate stringency is defined by the FBI as a search that requires all alleles to match. The FBI further insists a minimum of 10 of Winter 2019 | FLORIDA DEFENDER • 25 the CODIS core loci is required for searching forensic DNA profiles at the National DNA Index System level. This standard is recommended for merely identifying familial relationships, such as in missing persons cases. Evidence presented in a capital murder trial can and should be no less precise.

Further, the occurrence of allelic dropout cannot be independently verified — the only evidence that this phenomenon occurred is the “inconsistency” that it purports to explain. Obviously, there is another possible interpretation that is more favorable for the accused—i.e., that police arrested the wrong man. According to the Symposium, supra, the CPE/CPI approach for reporting an inclusionary statistic requires that all alleles be observed in the evidence sample. Where the laboratory is assuming that the collected sample is a mixture of two or more contributors, then there may be allelic dropout and all alleles may not be fully represented.

This is not in compliance with either SWGDAM or CPE/CPI standards. [CPE/CPI is also known as the “Random Man Not Excluded” formula for statistical approaches regarding mixture interpretation].

The arguments made by these experts and derived from the evidentiary standards of the FBI dictate that evidence which places such tremendous consequence upon inferences made by laboratory technicians should be considered by the courts to be a matter of admissibility, not a matter of weight. The FBI, SWGDAM, CPE/CPI, and the leading experts in the field of DNA identification agree that allelic dropout and samples containing less than a 13 of 13 allelic match are not sufficient enough to be used as evidence. Such evidence, which relies so heavily upon inferences, does not meet the standard of the second and third prongs of Fed. R. Evid. 702; nor does it meet the standard of most state-adopted evidentiary rules. It further fails to meet the “generally accepted” standard set forth in Frye and the “scientific knowledge” standard of Daubert, and therefore must be excluded.


Painting the Target Around the Arrow. 

A study performed by the worldrenowned DNA authority, Dr. Greg Hampikian, presented empirical data suggesting that DNA mixture interpretation is subjective. When 17 North American expert DNA examiners were asked for their interpretation of data from an adjudicated criminal case in that jurisdiction, they produced inconsistent interpretations. Furthermore, the majority of the “context free” experts disagreed with the laboratory’s pre-trial conclusions, suggesting that the extraneous context of the criminal case may have influenced the interpretation of the DNA evidence, thereby showing a biasing effect of contextual information in DNA mixture interpretation. The mixture DNA from the aforementioned adjudicated case was examined by experts in the real criminal case, and their analysis and conclusions were that the suspects that were identified by the cooperative assailant could not be excluded from being contributors to the mixture. The establishment of this corroborating fact was essential to the prosecution of the suspects who claimed innocence. Under the law of that state where this act occurred, the testimony of the admitted rapist would not be admitted without corroborating evidence. Therefore, the DNA conclusions were critical to prosecution. If the suspects were excluded by DNA, or even if the DNA was “inconclusive,” the incriminating testimony of the admitted rapist would most likely not be allowed. As potentially biasing as this domain irrelevant context was, if DNA was totally objective it should not have affected their analysis.

In this study Dr. Hampikian and his team took the original materials used by the DNA examiners that concluded that the suspect cannot be excluded, and presented them to 17 other DNA examiners, “context free.” The team asked the 17 independent DNA examiners to examine the DNA mixture along with DNA profiles of the victim and three suspects (one of the suspects, suspect 3, was the point of interest, as he was determined as ““cannot be excluded” by the DNA examiners who examined his DNA within the potentially biasing context). In regard to suspect three, the results obtained from the 17 independent DNA examiners varied. One examiner concluded that the suspect “cannot be excluded,” 4 examiners concluded “inconclusive,” and 12 examiners concluded “excluded.” The results are revealing in two respects: First, the fact that the 17 DNA examiners were not consistent in their conclusions, by itself, suggests that there is an element of subjectivity in DNA interpretation. If it was totally objective, then all the examiners would have reached the same conclusion, especially since they all work in the same laboratory and follow the same interpretation guidelines. The observed inconsistencies within the 17 examiners who conducted their analysis on the identical evidence, “context free,” demonstrated subjectivity in DNA mixture analysis, which may reflect individual differences (e.g., training, experience, personality, and motivation). It is interesting that even using the “gold standard” DNA, different examiners reached conflicting conclusions based on identical evidentiary data. Second, comparing the data between examiners, those from the context free condition to those who were exposed to the extraneous context condition, it is possible that the domain irrelevant information may have biased their interpretation. The DNA analysts who concluded that the suspect cannot be excluded within the biasing context of the criminal case, are in sharp contrast to the vast majority of examiners who examined the same evidence without this biasing context. Only 1 (out of 17) gave the same conclusion as the original analysts, 16 other examiners reached a different and conflicting conclusion (either “exclude,” 14 examiners, or “inconclusive,” 4 examiners). Thus, the extraneous context appears to have influenced the interpretation of the DNA mixture.

Consistent with this level of acceptance in the scientific community, the courts in the United States and elsewhere equate identity with DNA profiles that include complete allelic data from 13 or more of the standard short tandem repeat loci (STRs). However, in cases where low numbers of template molecules are amplified, or where complex mixtures are analyzed, subjective conclusions are made by analysts. This is evidenced by Dr. Hampikian’s study; however, one cannot estimate its magnitude and impact without more empirical studies.

That study is further evidence that laboratories will try to “paint the target around the arrow” when assuming the police have apprehended the “right man.” They do so by using mixed DNA samples to find matching alleles and use unfounded reasons such as allelic dropout to explain the lack of an acceptable match. This illustration is consistent with evidence which should not be admissible under any circumstances in any jurisdiction. As such, this partial DNA from a mixed source must be excluded as a matter of law.


A partial DNA specimen which originated from crime scene evidence containing DNA from more than one contributor has been shown to be unreliable at best. The FBI recommends not even using such evidence as an identifying tool when simply attempting to locate a next-of-kin. Because the data is unreliable, the Frye and Daubert standards, as well as the second and third prongs required for the admittance of evidence by Fed. R. Evid. 702 are not satisfied when such evidence is submitted in a prosecution where one’s liberty is at stake. Further, allelic dropout has been shown to be nothing more than an inference made to explain the lack of evidence at the laboratory level. When allelic dropout was used to explain the lack of 13 of 13 matches, a study was conducted. A database of 649 people were screened at all 13 loci. Over 5 million combinations of matches were made at 4 alleles or less. Imagine how many individuals in the world may be an allelic match at 2 of 13 alleles.

The state crime labs consistently fail to provide statistical analysis (which is required by the FBI, SWGDAM, and CPE/CPI) necessary to answer this question, yet courts consistently allow the prosecution to continue because this scientific “evidence” is rarely challenged and because the courts simply don’t have the correct data in front of the

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2 Fed. R. Evid. 702 states a witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if (c) the testimony is the product of reliable principles and methods.

3 According to Daubert v. Merrel Dow Pharm., 113 S.Ct. 2786 (1993), “Frye made ‘general acceptance’ the exclusive test for admitting expert scientific testimony. That austere [Frye] standard, absent from, and incompatible with, the Federal Rules of Evidence, should not be applied in federal trials.”

4 FBI Laboratory Services, SWGDAM Recommendations to the FBI Director on the “Interim Plan for the Release of Information in the Event of a ‘Partial Match’ at NDIS,” 2012.

5 Recommendations to the FBI Director, supra, at Recommendation 1.

6 Recommendations to the FBI Director, supra, at Notes.

7 William C. Thompson; Simon Ford; Travis Doom; Michael Raymer; and Dan E. Krane, “Evaluating Forensic DNA Evidence: Essential Elements of a Competent Defense Review,” The Champion, National Association of Criminal Defense Lawyers, p. 16, April 2003.

8 Mixture Interpretation: Using Scientific Analysis. 22nd International Symposium on Human Identification. Washington D.C.,

October 3, 2011.

9 Symposium, supra.

10 Symposium, supra.

11 W.C. Thompson, “Painting the Target Around the Matching Profile: The Texas Sharpshooter Fallacy in Forensic DNA Interpretation,” Law, Probability and Risk, 8:257-276 (2009).

12 Interpretation Guidelines, supra, at Interpretation of DNA Typing Results 3.2.

13 The Genetics of Innocence: Analysis of 194 U.S. DNA Exonerations.

14 Interpretation Guidelines, supra, at Glossary.

15 FBI Laboratory Services, SWGDAM Interpretation Guidelines for Autosomal STR Typing by Forensic DNA Testing Laboratories, 4.6.3, (2012).

16 Fla. Stat. §90.403.

17 Steverson v. State, 695 So.2d 687, 688-89 (Fla. 1997).

18 McDuffie v. State, 970 So.2d 312, 327 (Fla. 2007).

19 See State v. Meador, 674 So.2d 826 (Fla. 4th DCA 1996), which held “While officer can testify to results of observations of field sobriety tests, the terms “pass,” “fail,” and “points” should be avoided since the terms give an unwarranted aura of scientific validity.”

20 Evaluating, supra, quoted from Thompson, Ford, Doom, Raymer and Krane.

21 FBI Laboratory Services, Frequently Asked Questions on the CODIS Program and the National DNA Index System, 2012.

22 Frequently Asked, supra.

23 Evaluating, supra, quoted from Thompson, Ford, Doom, Raymer and Krane.

24 “Subjectivity and Bias in Forensic DNA Mixture Interpretation,” Science and Justice, 51:204-208.

25 “Subjectivity and Bias,” supra, quoted from Dr. Hampikian.

26 “Subjectivity and Bias,” supra, quoted from Dr. Hampikian.

27 “Subjectivity and Bias,” supra, quoted from Dr. Hampikian.