Posts Tagged ‘fingerprints’

 

Fingerprint brushes could transfer touch DNA, study says

Monday, February 15th, 2016

Locard’s Principle of Exchange has been an absolute fundamental in criminal forensics for a century. The concept that the perpetrator will always take traces of the victim and the scene with them, while leaving traces of themselves in exchange, is the basis of all modern investigation.

However, the principle has gotten a little more complex with how sensitive DNA tests have become in recent years. Secondary transfer of human DNA has been demonstrated through handshakes. Now, a study has found that fingerprint brushes used at crime scenes to find latent prints could actually be picking up and then dropping genetic material in different locations.

The DNA was found in low-copy number techniques, according to the Journal of Forensic Sciences study, authored by forensic scientists at Florida International University.

“The dusting of latent prints may dislodge cellular debris from the latent print or substrate. That debris then adheres to the brush,” they write. “This brush is then used on another item of evidence, or at another crime scene, where it is subject to the same mechanical maneuvering and where it can dislodge cellular debris, leaving traces of biological evidence not pertinent to the evidence being handled.”

The more-exacting polymerase chain reaction process of amplification led to detection of DNA transfer: in 5 of the 12 samples in the 28-cycle process, and a startling 10 of 12 tests using a post-PCR cleanup process.

But the risk of false associations based on the contaminated DNA was only “moderate,” considering their laboratory conditions and analytic procedures, they conclude.

Since the possibility exists, however, standard protocols to handling latent prints before DNA testing needs to be established to eliminate the possibility of false results.

“Under LCN conditions, it may be possible to obtain DNA results that are not relevant to the case due to a secondary transfer by fingerprint brush contamination,” they conclude. “Comparisons to these results may lead to matches or inclusions thereby potentially producing false associations between the evidence and crime scene.

“Improper procedures may lead to false exclusions or false association between evidence and crime scene,” they add.

Bruce McCord, the lead author of the study, and his team at Florida International University were the recipients of the most National Institute of Justice awards during 2015, totaling $1.5 million – partly for their DNA analysis work, and also for studies into forensic chemistry and other topics.

McCord told a university publication that he was working on a DNA analysis method for on-scene results within six minutes.

SOURCE: This article was first published online by Forensic Magazine on 12 February 2016 – http://www.forensicmag.com/articles/2016/02/fingerprint-brushes-could-transfer-touch-dna-study-says

Can you determine race from a fingerprint?

Wednesday, September 30th, 2015

For years, forensic scientists have studied differences between latent fingerprints and have used this information to identify unique patterns. Now, a new study takes a closer look at the minutiae of fingerprints and has come to an astounding conclusion: latent prints can provide clues to a person’s race.

The study in the American Journal of Physical Anthropology takes a new anthropological angle on a key identification method which may hold promise for law enforcement – and which has already attracted attention from several agencies, according to the researchers from North Carolina State University.

“By studying variation between groups, such as sexes and ancestry groups, on the basis of minutiae, this study provides information that is useful to latent fingerprint examiners,” said Nichole Fournier, lead author of the study, in an email to Forensic Magazine. “The results show that minutiae can tell us the probable ancestry of a person who leaves behind a latent fingerprint.”

The right index fingers of 243 individuals – split equally by gender, and between African-American and European-American backgrounds – were analyzed in the study. Level 1 details are pattern types and ridge counts.

But researchers focused on the Level 2 differences, which include bifurcations, where the ridge splits. These more-detailed factors were cross-referenced against the group’s identities. Gender did not result in significant differences in the prints – but race did, the scientists found.

“This is the first study to look at this issue at this level of detail, and the findings are extremely promising,” said Ann Ross, a North Carolina State professor of anthropology and the senior author of the study.

“But more work needs to be done,” Ross added. “We need to look at a much-larger sample size and evaluate individuals from more diverse ancestral backgrounds.”

The work, in part, answers the call of a scathing 2009 National Academy of Sciences report which called for further scientific research into forensic evidence collection and analysis, Fournier said. Fingerprints were one of the disciplines which were singled out in that report.

“Our study was in response to that call to action,” said Fournier.

Previous work by anthropologists had not been relevant to forensics because pattern type is not a trait used in fingerprint comparisons to identify latent prints at crime scenes, she added.

But now a more-complete picture of fingerprints could be coming into focus, Fournier said.

“This information is valuable evidence to corroborate the conclusion of a match based on a point-by-point comparison by a latent fingerprint examiner,” she said.

Other recent fingerprint advances have used mass spectrometry to hone in on trace amounts of material on the fingerprint, including narcotics, or hormones which could indicate gender. But they have not focused on the print pattern itself.

SOURCE: This article was first published by Forensic Magazine on 29 September 2015