Category Archives: Trace & DNA

Tools for Improving the Quality of Aged, Degraded, Damaged, or Otherwise Compromised DNA Evidence

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.

Read the full paper Here

New Study on Survivability of DNA Evidence

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):

Trace Evidence: Hair

by Kathy Steck- Flynn

Edmond Locard was the founder of the Institute of Criminalistics at the University of Lyon in France. Locard believed that that when on person came in contact with another person or object a cross transfer of minute particles occurred. This theory became known as the “Locard Exchange Principle”. Locard believed that crimes could be solved by inspecting the “dust particles” carried to and from a scene. This science is known today as criminalistics and has led to the rise of the forensics laboratory (from Mount Royal College background notes FORE 4407 section 3: Unit 4) Francois Goron, head of the French Surete, seems to be one of the first modern investigators who tried to use hair to identify a killer. In his first case hairs found clutched in a dead woman’s hand could not be identified as human simply because there was no information on the subject.

The inability of the scientific community to distinguish between animal and human hair raised interest in the analysis of hair. In the years that followed researchers began to collect information about the structure of human and animal hair (Block, 1979). In 1899, several years after his original failure, in a case known as “L’affaire Gouffe” Francois Goron was able to establish that a murder victim’s hair had been dyed. Establishing this simple fact led to the identification of Gouffe’s body and subsequently to the arrest of his killers (Block 1979). Francios Goron had successfully used forensic hair examination to solve a crime. Continue reading

Interpretation, Collection and Preservation of Glass Fragments

By Kathy Steck-Flynn

A man is found dead in an abandoned house. Upon examination the medical examiner finds that the man was killed by a single gunshot to the head. Three local teens where observed near the house two days earlier. They are picked up and questioned by police. When pressured, the teens admit to having stolen one of the boys’ father’s guns. They had taken turns shooting at the windows of an abandoned house.

The teens admit that John shot the gun first, then Jay and last was Fred. At the scene the investigators find three bullet holes in a window. They analyze the angle of each bullet hole in relation to the victim and find that the bullet which passed through the far right side of the window pane is the one which fatally wounded the man. Continue reading

Condom Trace Evidence: A New Factor in Sexual Assault Investigations

By Robert D. Blackledge, M.S.
Mr. Blackledge is senior chemist at the Naval Criminal Investigative Service Regional Forensic Laboratory in San Diego, California.

This Article Originally Appeared in the FBI Law Enforcement Bulletin, May 1996.

(Offenders are changing the nature of sexual assault investigations by wearing condoms.)
In an age filled with potentially fatal sexually transmitted diseases, more and more individuals practice safe sex. Even perpetrators of sex crimes have begun to wear condoms.1 It is not likely that a fear of disease prompts this behavior. Rather, just as a burglar dons gloves to avoid leaving fingerprints, sexual offenders now wear condoms to avoid depositing seminal fluids. Continue reading

Serological Evidence in Sexual Assault Investigations

By Robert R.J. Grispino, M.A.
Special Agent Serology Unit, Laboratory Division FBI Headquarters

This Article Originally Appeared in the FBI Law Enforcement Bulletin, October 1990.

NOTE: The following article presents a purely scientific approach to sexual assault evidence collection. The scientific step-by-step procedures that are explained here should always be accompanied by supportive treatment of the victim. It should also be noted that the investigating officer will be responsible for both overseeing the execution of the medical procedures described and managing the collection of the physical evidence.

Police officers throughout the United States routinely handle and oversee sexual assault investigations. Yet, these officers rarely receive training on the proper methods to be used for sexual assault evidence collection and preservation. As a result, valuable physical evidence may either be overlooked or inadvertently allowed to deteriorate biologically. This article establishes proper evidence collection and preservation protocol in sexual assault matters and demonstrates how modern forensic serology can aid in the eventual successful prosecution of the assailant. Continue reading