Editor’s Page DNA in Forensics by Robert L. Stevenson T
he proliferation of forensic DNA testing and databases by state and local jurisdictions was recently reported by Joseph Goldstein in The New York Times.1
For years, the FBI’s combined indexing
system (CODIS) has maintained three national registries of human DNA records. One is a registry of convicted felons, the second is for evidence from crime scenes, and the third is of DNA of unidentified persons.
However, law enforcement is responding to needs at the local level and to incentives to create their DNA databases with much larger scope. The zeal shown by local officials should be balanced with the need to make sure the evidence is analyzed accurately and is available to both the prosecution and defense for critical review. America’s legal system will not survive if it is widely perceived as delivering biased justice.
Local programs differ in scope. Most examine DNA samples from crime scenes. In one case, a doorknob was sampled in a residential burglary, and then DNA samples were requested from the residents of the home. All of the samples were placed in the local registry. There is no way that information can be removed. Worse, it may be shared with other locations without the knowledge or approval of the donors. Simply being listed in a registry may precipitate further questions in a traffic stop, etc.
Denver maintains a local database. The district attorney uses a software program to identify relatives of a person with DNA collected from a crime scene. Potentially, this could be submitted to a grand jury to question family members about the identity and location of other family members, which would probably include the person with the target DNA. Failure to cooperate could potentially lead to imprisonment for failing to cooperate with a grand jury.
In 2013, analysis of DNA is probably the most golden of all the gold stan- dards in forensics analysis. Each of us is different, and the difference is programmed by our unique genetic code. The exception is identical twins and triplets, who share identical genomes.
Still, for identification, many, if not most, think that each of us is uniquely defined by our DNA. DNA may be more definitive for identification than our fingerprints. Several test modes are used to characterize the DNA of a particular individual, including variable number tandem repeats (VNTRs); short tandem repeats (STRs); and Y chromosome STR, which focuses on the Y (male) chromosome in semen.
Even with this, the National Academy of Sciences, in its 2009 report, warned that “errors do occasionally occur.” These are usually traced to differences in interpretation, particularly when the sample is a mixture; failure to process the samples correctly; laboratory contamination; low sample amount; and differences in test protocols.
Plus, DNA testing is not infallible. For example, recall the confusion that resulted when it was reported that chronic fatigue syndrome (CFS) was related to human retrovirus XMRV in prostate tissue. There did not seem to be a biochemical explanation. Ultimately, the correlation was traced to a common primer DNA sequence with 99% homology. Initially this was interpreted as having a common origin or connection. Further work has shown that the conclusion is probably not valid.
Advances in molecular biology will probably uncover other ambiguities that may affect the validity of a particular DNA test. For this reason, the Innocence Project recommends that the DNA evidence be preserved for as long as the person is subject to incarceration, parole, or registration. Further, all records should promptly be destroyed in the event of exonera- tion or pardon.
Laboratories entering DNA profiles into CODIS must meet accreditation and use validated protocols. Proficiency testing is mandatory. Analysts are required to have at least a bachelor’s degree. The technical leader of the lab must have advanced training.
FBI reporting guidelines require: 1) a description of the evidence, 2) a list of the loci analyzed, 3) a description of the test protocol, 4) results, 5) conclusions, and 6) an “interpretative statement” concerning the infer- ence supported by the analysis.
The report by Goldstein1 is disturbing since there is no assurance that
the local databases have been gathered from trustworthy sources. Trustworthy sources include labs that collect and report results according to validated protocols. The staff also needs to be trained and motivated to deliver accurate results in a believable, impartial manner. This is one more example showing the need for a national program as proposed for a Forensic Laboratory Improvement Act.2
Errors in reporting in the forensics lab The forensics laboratory has a unique requirement to make measure-
ments and report results accurately. The lab can also offer interpretation of the results, but opinions from the technicians need to be recognized as opinions, and these are usually based upon experience. The labora- tory may proffer a set of statements that conclude, for example, that the defendant was present at the scene and/or had fired a gun:
• “Gunshot residue was found on the defendant’s gun hand. This is consistent with the defendant having fired a gun recently”
• “The fingerprint of unburned powder on the gun matches the residue on the suspect’s shooting hand”
AMERICAN LABORATORY • 4 • SEPTEMBER 2013
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60