‘…the “growing debate among the scientific and legal communities” regarding the use of the terms “identification” or “individualization” in court to associate “an item of evidence to a specific known source.”‘
‘…the dilemma this scientific transition is causing for veteran forensics experts. “Examiners in some forensic science disciplines have been trained that if you aren’t certain about your result, you don’t say anything,”‘
‘”These people have been trained another way, and some view this effort as ‘You’re asking me to do a less competent job, because you’re asking me to pretend I’m uncertain when I’m certain, and you’re asking me to testify when I’m not certain.’
By Michael M. Cox, Ph.D., Evelyn M. Mercer
Published by the NIJ
Almost every day, DNA samples are collected from the scenes of crimes or disasters that are too degraded for standard forensic DNA analytical procedures. This fact represents an ongoing impediment to law enforcement and victim identification efforts. Many law enforcement agencies also possess archived crime scene evidence from cold cases that are decades old, in which the DNA has become too damaged to analyze. The major problem in these samples is the presence of DNA double strand breaks. The purpose of the work carried out under grant 2010-DN-BX-K190 is to develop a new method to repair double strand breaks in forensic DNA samples, as a pretreatment for the standard STR analysis protocols. As part of this effort, we have also developed reproducible procedures for the artificial degradation of human DNA samples, using ionizing radiation to inflict a DNA damage profile that reprises that of a typical degraded forensic sample. Using this type of DNA as a test bed, we have developed a protocol that is successful in increasing/restoring missing or substandard signals at two STR loci. The protocol utilizes the bacterial RecA protein, single-stranded DNA binding protein (SSB), and bacterial DNA polymerase I, in concert with a targeting oligonucleotide. The reactions promoted by these reagents effectively restore damaged DNA flanking a particular STR locus. With the most developed protocol, signal restoration is successful approximately 20% of the time. With a few exceptions, the restored signals are accurate. The artifacts arising in the exceptions have been traced to the targeting oligonucleotides. Efforts to further develop this technology are continuing, focused on new RecA protein variants that increase signal strength and re-designed targeting oligonucleotides.
We have also been successful in demonstrating proof of principle in efforts to recover targeted DNA segments and remove them from bulk DNA in an effort to concentrate them and eliminate conditions that could inhibit STR amplification.
Article authored by: Stephen Michielsen, Michael Taylor, Namrata Parekh, Feng Ji
Bloodstain pattern analysis, BPA, on hard surfaces (such as walls, tables, appliances, hardwood floors, etc.) has grown into a science-based investigative tool that can help determine scenarios that are consistent with or counter to the events described by witnesses or suspects. At the vast majority of crime scenes involving a bloodletting event, textiles are present as apparel, household textiles (sheets, towels), upholstery, carpets, and so forth. Yet, the science of BPA is not able to render the same level of confidence in the analysis as on hard surfaces due to the complex structure of textiles and their ability to wick liquids. In the work described herein, a detailed examination of factors that affect BPA on two textile fabrics, an unbalanced 130 x 70 plain woven 100% cotton bed sheeting fabric (often referred to as a 200 thread count bed sheet) and a 100% cotton jersey knit T-shirt fabric.
During this study, both porcine blood and several synthetic blood recipes were used. The dynamic impact tests (time after impact < 100 ms) used porcine blood, while most wetting and wicking experiments employed synthetic blood (time after impact > 100 ms). Most of the synthetic blood recipes examined performed badly. Either they would not dry or they did not wick into the fabrics, but remained on the surface. A synthetic blood recipe from the American Society for Testing Material (ASTM test method F1819-07) performed well, but its viscosity and surface tension were both lower than typical human blood. Thus, this recipe was modified to lie within the range of surface tension and viscosity of human blood. It was used for the majority of wicking and wetting experiments. In a preliminary comparison, it was found that synthetic blood SB5 behaved similarly to porcine blood in many aspects, but the SB5 stains were significantly larger than the porcine bloodstains. We attributed this difference to the presence of red blood cells, which behave as particles, as well as plasma, which behaves as a liquid, in porcine blood. SB5 is an aqueous solution and behaves entirely as a liquid. Continue reading →
A new study published by the NIJ, demonstrates positive recovery of DNA for up to 10 days following intercourse. Given various circumstances that may lead to delays in reporting or testing, it’s good to know that current testing methods may still yield results even with a substantial delay.
The study can be accessed here (in .pdf format): https://www.ncjrs.gov/pdffiles1/nij/grants/248682.pdf
Interesting historic video on crime scene investigation and forensic science. I have a copy as well, that I purchased on DVD from the National Archives. The date on the original is a bit unclear, but it appears to have been made around 1960. It should be noted that some of the practices shown are no longer up to date, and that current safety precautions are not in use. It’s still interesting from a historical standpoint.
Just what is the impression of forensic science held by members of the general public (our pool of jurors)? If they believe everything they see on TV or in the movies, they are being sadly misled. Our local attorneys believe that, at the very least they have been generally misinformed about the likelihood of finding fingerprints by exposure to the media. Because of this I will be in court in the coming weeks giving testimony on the difficulties of recovering fingerprints from duct tape… Of course the same attorney moments later mentioned how unusual it is to recover fingerprints from guns- Which he felt had good surfaces for recovering fingerprints. (I re-educated him on this point, as guns have generally lousy surfaces, not to mention all the handling involved in firing/recovering/and making safe prior to processing).
It has been my experience that not only do members of the general public have a lack of understanding of forensic science, but that police officers, detectives, prosecutors and judges are often not much better. I think this trend is likely to continue as long as forensics is misrepresented in the media. People tend to refer to personal experience when assessing the value of new information, and when the personal experience with forensic science is “I was watching Law and Order on TV the other night and they…. ” Continue reading →
“Wizard’s First Rule: people are stupid…given proper motivation, almost anyone will believe almost anything. Because people are stupid, they will believe a lie because they want to believe it’s true, or because they are afraid it might be true.”
-Terry Goodkind, Wizard’s First Rule,Tor Books, 1994.
“To a jury about to convict a man of a capital crime, any doubt is reasonable.”
-Commentary on the O.J. Simpson trial.
In recent months I have had two different District court judges, lower two different counts of Home Invasion to either Unlawful entry, or Trespassing. Their reasoning? One said that even though we identified the defendant’s fingerprints on an item in the residence which was handled, but not taken. Even though he had no business being in the residence- because there were other fingerprints which we did not identify (we eliminated a number of prints belonging to the owner and his family) we could not show that the defendant had any intent to commit a larceny, one of the “unidentified” persons could have committed the larceny. Continue reading →