The Golden State Killer left havoc behind wherever he went in the 1970s and 80s in California. Last year, police said they had their guy, nearly 50 years after his first known crime, bringing closure to a string of cold cases including hundreds of home invasions, dozens of rapes, and more than a dozen murders. The accused is Joseph James DeAngelo, now age 73 and being held without bail in a California jail, charged with 13 counts of murder and 13 counts of sexual assault. But how did the police finally make the connection, and will it be enough to convict him?
In this fascinating landmark case, investigators sequenced DNA obtained from crime scenes all thought to be the work of the Golden State Killer. They used this decades-old evidence, which had been in storage, to develop a genetic profile. That profile was then plugged into an online genealogy database. Using that database, investigators were able to find distant relatives that shared the same DNA, essentially tracing their way to his door through DeAngelo’s lineage. Police claim to now has a 100% DNA match between their stored crime scene evidence and DeAngelo’s DNA.
But does DNA testing bring that same 100% level of certainty to this case? Our Los Angeles criminal defense attorney thought it would be interesting to look at DNA reliability a bit closer.
DNA, or deoxyribonucleic acid, is found in most cells in the body, including in the bone, in the blood, and in the skin. DNA contains genetic info that determines things like eye color and height. There are literally billions of letters of genetic code in DNA, and astonishingly enough, 99.9% of the genetic code in any DNA sample is an exact replica of the DNA of every human being. There is approximately 0.1 percent of the genetic code that makes each of us unique.
When DNA is tested, analysts look at a dozen or more genetic markers located in the genetic code. These markers help to identify differences and similarities in humans. The more markers examined, the higher the accuracy of the DNA test. However, the probability of two people who are unrelated having matching profiles of DNA is around 1 in a billion.
As our legal team knows, accurate identification by DNA depends on several factors—perhaps the most important among them being the quality of the tested DNA sample. Other factors include whether the sample in question was properly prepared and if the analyst interpreting the results does so appropriately.
When DNA is matched to a suspect, it tells us the identity of the suspect, but it doesn’t really do anything to tell us how the DNA arrived at the location where it was discovered. Skin cells are continually shredded, trace DNA is left on things that we touch. DNA can even travel by wind and land miles away from where it was left.
Will DNA from nearly 50 years ago be enough to put the Golden State Killer away? This case is still playing out in court, so it will be interesting to see how big a role DNA plays when DeAngelo goes to trial.
Facing legal trouble? Contact Okabe and Haushalter now to discuss your case with our Los Angeles criminal defense attorney.