Forensic genealogy has a starring role in media reports about the apprehension of Idaho quadruple murder suspect Bryan Kohlberger.

The reported match of DNA evidence collected from a button snap on a knife sheath left at the murder scene to a sample taken from the suspect’s father’s trash in Pennsylvania demonstrates how far the field of forensic genetics has come in the last few decades, says Northeastern University criminologist James Alan Fox.

But Fox says that while forensic genealogy is a powerful tool, its usefulness in the majority of homicide investigations is limited—and probably wasn’t even necessary in the Idaho case.

Forensic genealogy is when law enforcement couples DNA analysis with traditional genealogy research to come up with leads for unsolved violent crimes, according to the U.S. Department of Justice.

Advances in DNA technology and the proliferation of ancestry DNA research databases have made forensic genealogy a powerful tool in solving cold case crimes, perhaps most famously with the arrest of Joseph James DeAngelo in 2018 for the decades-old Golden Gate killings in California.

Investigators used DNA samples taken from the crime scenes to compare against DNA sequences in a public database to help narrow down DeAngelo as a suspect, eventually fishing a tissue out of DeAngelo’s rubbish to make a match.

In the recent apprehension of Bryan Kohlberger for allegedly murdering four University of Idaho students Nov. 13, investigators also used trash, this time taken from Kohlberger’s family home in Pennsylvania, to create a genetic link between DNA collected at the scene and the suspect.

According to the affidavit applying for an arrest warrant, the DNA profile created from evidence on the Ka-bar knife sheath laying on a bed next to one of the victims linked the DNA found in the family’s garbage to Kohlberger’s father with more than 99% accuracy.

The DNA evidence on the knife sheath could have been blood, saliva, sweat, hair or other biological evidence, Fox says.

But he says he believes the genealogical approach and garbage sleuthing was not necessary in this case.

Investigators probably had more than enough evidence to take Kohlberger into custody. It included a surviving roommates’ description of a masked man with bushy eyebrows, the presence on scene of a white Hyundai Elantra similar to Kohlberger’s and cell phone records allegedly showing that the suspect had repeatedly stalked the victims in their Moscow, Idaho, residence.

“They had him in mind long before the genealogical search,” Fox says.

“In this particular case, they would have solved it anyway” and would have been able to obtain  Kohlberger’s DNA once he was in custody, Fox says.

He says forensic genealogy won’t be of use in solving most murders because two-thirds of all homicides are by firearms.

“A bullet doesn’t have DNA. If someone’s shot, there’s no physical evidence from the perpetrator, assuming the shooting is from some distance,” Fox says.

Inclusion of Kohlberger’s father’s DNA in the application for Kohlberer’s arrest was evidence of the thoroughness of the investigation into the murders that shocked a nation, Fox says.  

“It was just one more piece of the puzzle,” he says.

The use of genetic material as an investigation tool has come a long way since the 1980s, when  states began passing laws mandating the collection of DNA samples from offenders convicted of sexual and other violent crimes.

When Fox served on a task force investigating the Gainesville murders of five college students in Florida in 1990, the only DNA samples available for comparison purposes were from criminals or criminal suspects in databases such as the FBI’s CODIS, the Combined DNA Index System, which itself has grown substantially over the years.

“We didn’t have familial DNA procedures,” he says. 

But many serial and mass killers—such as DeAngelo, who was convicted of murder and rape in 2020—do not have an official crime footprint.

“There’s a myth that these individuals have a history of criminality or mental illness. Most of them do not have a criminal record,” says Fox, who maintains a database on mass killings that went public in August. 

Approximately two-thirds of public mass killers lack a criminal record or history of involuntary commitment, which is why family ancestry research material has served as such an important tool in solving cold cases, he says.

“Most mass killers—as opposed to serial killers—are apprehended quickly without the aid of DNA,” Fox says.

When five college students were killed over four days in Gainesville in 1990, DNA technology was still in its infancy. 

These days, forensic investigators can get loads of genetic information from a single hair; back then pubic hairs left on the scene were mainly used to rule out suspects, Fox says. 

The latter was used to exclude a suspect arrested early on and whom Fox never believed met the psychological profile of the killer.

Hired as a consultant to the task force investigating the murders, Fox believed there was a possible connection to the triple murder of a 55-year-old man, his daughter and grandson in Shreveport, Louisinana, based on the lengths the killer went to to clean up evidence of sexual assault.

After Danny Rolling, a man who lived near the Louisiana victims was arrested for robbing a grocery store about 30 minutes away from Gaineville, investigators suspected a possible link to the student slayings and sampled DNA from a tooth that had been extracted from Rolling to make a DNA match, Fox says.

“Once something’s in the trash, it’s no longer yours,” he says. “You have no privacy rights to trash.”

That’s something Kohlberer, the Idaho suspect who was pursuing a Ph.D. in criminology, was likely aware of since he attempted to hide his family’s trash in a neighbor’s bins, according to a report by CNN. 

Improved technology means that investigators can use even smaller samples of DNA to create a genetic profile, says Fox, who, with Northeastern professor emeritus Jack Levin, wrote a book about the Gainesville murders, “Killer on Campus.”

Using DNA to solve crimes “is especially effective in cases where it’s very easy to tie the profile to the crime, like a single perpetrator sexual assault,” says Daniel Medwed, a Northeastern University School of Law professor. 

DNA can also be used to rule out a suspect, says Medwed, who specializes in defense cases. 

When it comes to forensic genealogy, people also have to remember that not everybody is in the genealogical research pool, Medwed says.

While researchers reported in the journal Science in 2018 that DNA ancestry searches can now identify most white Americans, not everybody has relatives with the funds and interest to submit saliva for DNA sampling, he says.

“There’s a randomness to who is and who is not going to be apprehended through forensic genealogy,” Medwed says.

“It’s one additional avenue for investigators to pursue, assuming you have DNA at the crime scene,” Fox says.

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