ASU forensics expert explains DNA tech being used in Guthrie investigation
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It’s been more than 30 days since Nancy Guthrie disappeared from her Tucson, Arizona, home, and with little physical evidence pointing to a suspect, investigators have turned to an advanced forensic method known as investigative genetic genealogy, or IGG.
The relatively new DNA method gained national attention in 2018 when it helped capture the Golden State Killer, and since then it has been used by law enforcement agencies across the country to help identify other violent offenders in cold cases and unsolved crimes.
To better understand how IGG works, how reliable it is and what other emerging DNA tools and technologies may shape the future of criminal investigations, ASU News spoke with April Stonehouse, an Arizona State University professor of practice in the School of Interdisciplinary Forensics.
The DNA analyst has extensive experience working with law enforcement and prosecutors to develop evidence that stands up to court scrutiny.
Note: Answers have been edited for length and/or clarity.
Question: You have 23 years of forensic experience analyzing crime scene evidence and conducting DNA testing. What kinds of cases have you worked on, and is there one that stands out as especially impactful?
Answer: As a forensic serologist and forensic DNA analyst, I have worked on many kinds of criminal cases including homicides, sex offenses, robberies, burglaries, arsons, criminal paternity cases and cold cases. There is one case that stands out as being particularly impactful: a Jane Doe cold case homicide from 1981 for which I performed the serology and DNA testing. With persistence and extensive serology testing, I was able to locate a source of DNA from the victim’s clothing that I entered into the national DNA database.
I received a CODIS (U.S. criminal DNA database) hit on an incarcerated Arizona offender. When interviewed, he had a picture of the victim in his prison cell. That photograph became the key that cracked the case. It appeared to have been taken on the East Coast, prompting investigators to search missing persons reports in that region. They located a match. Through forensic DNA analysis and investigative efforts, the victim was identified as Brenda Gerow. Giving her back her name and allowing her family to provide a proper burial was incredibly rewarding.
Q: Investigators in the Nancy Guthrie case are reportedly using investigative genetic genealogy (IGG), an advanced DNA technology that gained national attention after the identification of the Golden State Killer. Why would detectives turn to IGG in a case like this?
A: Detectives turn to IGG after a DNA profile doesn’t match anyone in the U.S. criminal DNA database. In the context of new cases, like in the Moscow, Idaho, murders, the perpetrator was so young and had never been convicted of a crime, so his DNA profile simply wasn’t in the U.S. criminal database.
In the context of cold cases, the perpetrators of these much older cases may simply not be in the U.S. criminal database because the database didn’t come into existence until the late 1990’s.
If there is no match in the criminal database, investigators may turn to ancestry databases in an attempt to identify relatives of the person who left DNA at the crime scene.
Q: For readers unfamiliar with it, how does investigative genetic genealogy work?
A: The process begins when conventional DNA typing, called short tandem repeat (STR), is performed on crime scene evidence. The STR DNA profile is developed from the evidence and searched in the U.S. criminal database to see if a match occurs.
If there is no match, investigators may then turn to IGG to identify the perpetrator. The DNA is sent for sequencing to examine, and single nucleotide polymorphisms, or SNPs, are tested. (An SNP) is a single base change in the DNA, and there are millions of these little changes in our DNA that make each person genetically unique.
Those SNP profiles are compared to public ancestry databases to locate relatives of the perpetrator. Once possible relatives are identified, genealogists build extensive family trees using public records, birth and death certificates, census data, obituaries and social media. By working forward in time through those family trees, investigators narrow down individuals who are biologically related to the DNA from the perpetrator and match the age, sex and geographic profile of the case.
Basically, IGG is another DNA route to identify a perpetrator by locating their relatives.
Q: How reliable is IGG, and based on what you know, could it advance the Guthrie investigation?
A: IGG combines DNA sequencing and genealogy, both highly reliable methods. DNA sequencing has been used since the early 1970s in research, medicine, outbreak tracking and agricultural improvements.
Yes, IGG could definitely advance the Guthrie investigation if evidence containing DNA from the perpetrator is identified and there is sufficient DNA to conduct the DNA sequencing needed for IGG.
Q: From a forensic standpoint, why has this case been so difficult to solve?
A: I think the case has been difficult to solve because the initial DNA results from the blood at the scene matched Guthrie. Investigators wouldn’t know that until after it had been DNA tested, and that takes time.
Once the results came back and it all belonged to the victim, the investigators needed to go back and do more testing in an attempt to develop a DNA profile of the perpetrator.
It may take multiple DNA testing cycles to find a profile from the perpetrator.
Q: Beyond IGG, what emerging DNA technologies or forensic tools are shaping the future of criminal investigations?
A: One major advancement is the installation of RAPID DNA instruments into booking stations. These automated systems can generate a DNA profile in less than 90 minutes. This allows law enforcement to DNA test a suspect while in custody and immediately search the national DNA criminal database for matches to unsolved criminal cases.
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