The methods used to investigate crime have evolved considerably over time… fingerprint analysis dates back to the 1880s, and the roots of forensic toxicology go all the way back to the first century, but most think of DNA evidence as the most effective tool in the investigator’s tool chest.
The use of DNA evidence is a fairly recent development in the world of criminal investigation, having only become practical in the 1990s, and despite its reputation as ironclad evidence, DNA has its shortcomings and law enforcement has continually pressed to advance investigative techniques even further. With the recent development of genealogical DNA analysis, sometimes known as genetic genealogy, they may have done just that.
What’s the difference between DNA evidence and Genealogical DNA Analysis?
In a criminal investigation, forensic investigators attempt to preserve and collect any DNA evidence that may have been left at the scene by the perpetrator. Law enforcement then compares the DNA profile generated by a forensic investigator to a database known as CODIS or, the Combined Index DNA System.
When the DNA Profile matches someone already in the system, law enforcement has a suspect to investigate, and they go about the business of building a case. If the suspect identified by DNA can be corroborated by other factors–the suspect lived in the neighborhood, matched an eyewitness description, or was found in possession of other incriminating evidence–the case is made.
The CODIS database contains DNA profiles from a lot of people–those who’ve been previously arrested, served in the military, etc… and although it is a huge database, it’s far from comprehensive. There are simply a lot of perpetrators who have never had their DNA sampled, so when investigators develop a DNA profile based on evidence left at a crime scene, they sometimes get zero matches back from CODIS and the DNA evidence becomes useless, because it doesn’t match anybody in the database. That’s where genealogical DNA analysis has proven to be a huge leap forward.
Genealogical DNA Analysis
Law enforcement’s most powerful tool owes its existence to the family tree and modern genealogy websites. As of this writing, more than 26 million people have taken an at-home DNA test and uploaded the results to one of the four major consumer genetics testing companies. The idea is to connect their DNA profile with others to discover family relationships and build a family tree. It’s a process that can be done much more quickly than the old method of tracking down birth, marriage, and death certificates.
It’s those public DNA databases that make genealogical DNA analysis possible, and the process usually consists of two primary steps: DNA phenotyping and genealogical matching.
DNA phenotyping involves developing a physical description of the suspect based on the physical characteristics encoded in DNA. The human genome was mapped in April of 2003, and in the time since, science has been able to develop techniques to “read” the information within… based on a DNA profile, we can know things about the suspected donor, like gender, hair color and eye color, for instance. Based on DNA phenotyping, law enforcement can generate a general physical description of the suspect they’re looking for.
Once they have a description of a potential suspect, the forensics lab uploads a sample of the suspect’s DNA to a public ancestry database in search of a genealogical match. When a match is made, investigators then proceed with the process of building a family tree based on the match until they find a person who could be the perpetrator.
The process can be very complex. Imagine this: a person in New York uploads their DNA to an ancestry site to learn more about their family history. Later, a detective uploads DNA from a potential suspect in a California crime and gets a genealogical match to the family tree of the person in New York. The California suspect and the person in New York share a common ancestor from the early 1800s. The detective must then go through the process of building out the family tree starting with the common ancestor… the common ancestor had 3 children, and those 3 children later had 12 children between them, and those 12 children had 27, and so on. Investigators build the family tree until they find a family line with someone who could potentially be the suspect–a person who matches the description developed through phenotyping, lived in the right place at the right time, was approximately the right age to have committed the crime, and so on.
The final step to secure an arrest involves recovering a DNA sample from the suspect identified through phenotyping and genealogical analysis, most commonly achieved through surveillance. Investigators stake out the suspect and wait until he or she discards something with their DNA on it–a straw, a cigarette butt, or a coffee cup, for instance. The DNA from the discarded item is tested, and if it matches the DNA recovered from a crime scene, the perpetrator has been identified and an arrest soon follows.
The process was first used successfully to identify and arrest the Golden State Killer in northern California in 2018. The process is not without its challenges, however, particularly with very old cold cases. In situations where the crimes themselves happened decades ago, the perpetrator is likely dead, making it very difficult to retrieve a DNA sample for matching purposes.
The case of the Zodiac Killer is one example. With crimes that took place between 1963 and 1970, the Zodiac is likely (but not certainly) dead, and left no DNA at his crime scenes. Investigators are undaunted, however, and in 2018, attempts were made to recover DNA from the stamps on letters the Zodiac sent to the media. If a DNA profile can be developed, authorities may be able to use genealogical DNA analysis to arrest the Zodiac if the perpetrator is still alive, or at least name him if he isn’t. When and if that happens, you can bet it will be big news.
The Results So Far
In the year after the arrest of the Golden State Killer, a single lab, Parabon Nanolabs, joined law enforcement and a genetic genealogist in investigating 200 cold cases through Genealogical DNA Analysis and the effort resulted in 55 more arrests nationwide. That is a staggering statistic, considering the majority of the cases were long cold.
The technology is still in its infancy, and you can bet it will become more effective as investigators hone their technique. It stands to be the most important development in criminal investigation since the advent of DNA as an investigative tool.
We’ll be discussing a lot of these cases in the near future, so check back for more.