0.12 ng, using the smallest DNA sample in history, the Las Vegas police cracked a 32-year old case of “cold storage”

“Gene Genealogy Criminal Investigation” has become one of the most powerful tools in the field of forensic medicine.


Before there was the Golden State homicide case , and later there was the prototype case of “Memories of Murder” . DNA technology has gradually become the backbone of criminal investigations.

But recently, the Las Vegas police still broke a record.

According to the official report, they used only 0.12 nanograms of DNA samples and about 15 cells to solve an old case that has remained unsolved for 32 years.


Official report:


Conventionally, DNA detection kits need to collect at least 750 nanograms of DNA samples.

In this case, the 14-year-old victim Stephanie Isaacson was strangled to death after being sexually assaulted in 1989. Regarding the murderer issue that everyone cares about, the police targeted the suspect’s cousin and finally identified Darren Roy Marchand as the murderer himself, but Marchand died in 1995 and was not convicted in this case .

Isaacson’s mother said at the press conference, “I am very happy that the police have found the man who murdered my daughter” and “I didn’t expect this case to be resolved eventually.”

Some netizens said, “Not all cases can be solved in the end, and I am very happy that this case can be closed.”


Some netizens also wrote in a message, “Justice is forever . 


Insufficient DNA collected, resulting in the case being “refrigerated” for 32 years 

Let us briefly review the case first.

On June 1, 1989, 14-year-old Stephanie Isaacson left home to go to school at about 6 in the morning. Isaacson did not return home after school that afternoon, and his family immediately reported missing to the police.

Later that night, her body was found in a clearing near Stewart and Nellis, and after examining the body, it was discovered that Isaacson was strangled to death after being sexually assaulted.

Since the amount of DNA collected at the crime scene was very small, only tens to hundreds of nanograms, the case was “refrigerated” for 32 years due to lack of conclusive evidence .


Until November 2020, the Las Vegas police received a donation from local resident Justin Woo, which was mainly used to deal with unsuccessful homicides with very few DNA samples.

On January 19, 2021, the Isaacson case was selected and the sample was sent to the Othram laboratory. On July 12, the Othram laboratory stated that because the DNA was less than 120 picograms and there were less than 15 human cells, they could only identify the suspect through the test program of genome sequencing .

Through genealogy research, the suspect was identified as Darren Roy Marchand, a Las Vegas resident, but he committed suicide in 1995.

According to the police follow-up investigation, Marchand was due in another Isaacson with the case were arrested, but the case was dismissed. The DNA and semen samples found in the Isaacson case can match the DNA found in this case. 

“Gene Genealogy Criminal Investigation” has become one of the most powerful tools in the field of forensic medicine 

What is going on with the DNA technology that has been so successful?

In 2018, “Genetic Genealogy Criminal Investigation” was listed by Science as a major technological breakthrough. The biggest contribution of this technology is that it achieves “fuzzy matching”.

In the past, after the police collected DNA from the crime scene, they had to accurately match the suspect in order to find the suspect. That is to say, the DNA of the criminal must be matched. However, gene genealogy technology allows the police to find the suspect’s distant relatives , so as to track down the prisoner.

Of course, there are two very important breakthroughs behind gene genealogy technology.

The first is the rise of public genetic databases. In the past, the DNA database of the police generally only contained the DNA of criminals with previous convictions, but nowadays, because ordinary people only need to spend a little money, scrape the oral mucosa with a cotton swab and send it to a professional company, they can test their own DNA. These data gradually accumulated, and a huge public gene database appeared.

The other is a method called “long-line family search” , which is also the key to fuzzy matching of gene genealogy. In the past, family searches through DNA comparisons could only match close relatives, while “long-term family search” can match individual DNA all the way to the third representative. The use of this method is largely due to the advocacy of some retired family history enthusiasts who have been trying to convince law enforcement officials for years that their technology can be used not only to find the biological parents of the adoptee, but also to a wider range of applications. the use of.


After the Golden State Killer case, the related technology has received widespread attention from the outside world and proved to be one of the most powerful tools in the field of forensic medicine.

In the following months, groups such as Parabon NanoLabs and the DNA Doe project identified at least 19 different unsolved case samples using this method , called the familial DNA test of the public database, which provided vital information for previously unsolvable cases. New clues.

Biotechnology innovation is affecting our lives

But we can’t help but still have some concerns about this.

For example, the police’s use of gene genealogy to solve crimes in criminal investigation has raised questions about privacy and security.

Some netizens said that users of genealogy websites did not realize that they would be involved in criminal investigations. Although websites such as GEDmatch revealed that files can be used to investigate violent crimes, FamilyTreeDNA, which cooperates with the FBI, directly positions itself as a means of hunting down killers, which is undoubtedly It is a wake-up call for many people: Should governments and companies obtain our genetic information? If so, what should they do with this data?


Apart from the law, individuals have little way to protect their genetic data. Even if an American has never undergone a DNA test, in the hands of an advanced genealogical detective, usually only the DNA data of his two third-generation cousins ​​identified from a drop of saliva, blood or semen can be known. .

In other words, if one offspring of 16 great-great-grandparents, at least 800 people are scattered in different corners of the world, and it is very likely that some of them have uploaded genetic data on GEDmatch-GEDmatch has about 1 million users.

According to a recent study, 90% of European Americans’ DNA will be identified through genetic lineage .

Different lawyers also have different opinions. Blaine Bettinger, an intellectual property lawyer who works with GEDMatch, believes that judges can decide to process clues from genealogy websites, just like evidence from Codis or Instagram.

Dr. Leah Larkin, from The DNAGeek’s DNA Analysis Service Center, believes that the technology violates the Fourth Amendment’s protections against illegal searches and seizures: “Since the police cannot break into the house for investigation without an arrest warrant, then This data should not be used—the private information in my DNA is much more than the information in my underwear drawer.”

Sacramento District Attorney Anne Marie Schubert created after the success in the Golden State in a murder genetic transfer genealogy units are considered these fears are unnecessary. “We won’t get people’s DNA in these genealogical databases,” she promised to get only information about the relationship between website users and suspects.

Thousands of criminal cases are on the one hand, and the future of genetic privacy on the other. It may never be answered whether the two are more important.

Related reports:




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