The Zodiac Killer murdered at least five people in the San Francisco Bay Area in 1968 and 1969. He then sent taunting letters to local newspapers including cryptogram puzzles as clues to his identity. One correspondence claimed he had killed as many as 37 people.

DNA at the crime scenes was basically non-existent. No blood or semen was left behind. The murder weapon itself (the killer would use a gun or a knife) was also never recovered. Even a rope used to tie one victim had been tested unsuccessfully for the killer’s DNA profile.

Then in December 1969, the Zodiac Killer sent a letter to San Francisco attorney Melvin Belli. On the envelope lies a postage stamp the killer licked more than 50 years ago and that could be the roadmap that leads investigators to his real identity.

There is always the possibility the Zodiac Killer did not personally lick the stamp for fear of incriminating himself but this is unlikely as DNA profiling would not exist for another 20 years.

Fast forward to the early 2000s when investigators were finally able to create a partial profile of the Zodiac Killer using this saliva sample. Although the profile is incomplete, they were able to rule out several long-time suspects including Arthur Leigh Allen in 2002.

The FBI enlisted cryptanalysts and code-breakers to help unravel the complex cipher but the case went cold for many years. Until finally in December 2020, an international three-person team of codebreakers, including an Australian mathematician, was able to decipher the message.

David Oranchak, Sam Blake, and Jarl Van Eycke revealed the message they found in the extremely complex note with 340 characters that became known as the ‘340 cipher’.

They revealed the secret message in a video posted to YouTube by Mr. Oranchak. It reads: ‘I hope you are having lots of fun trying to catch me. I am not afraid of the gas chamber because it will send me to paradice (sic) all the sooner because I now have enough slaves to work for me.’

Now more worldwide attention is returning to one of the most infamous cold cases, it could only be a matter of time before the Zodiac Killer is caught.

Hopes have been renewed for cold cases since serial killer Joseph ‘Golden State Killer’ DeAngelo was captured in 2018. Following a manhunt that lasted more than 40 years, familial DNA finally led investigators directly to him. He was 73-years-old at the time of his arrest. The Zodiac Killer is believed to be approx. 85-years-old.

Will investigators be able to decipher the serial killer’s identity using familial DNA? Well, that all depends if a relative (even a distant one) becomes curious about their own genetic profile.

How Familial DNA Catches Serial Killers

Between 1976 and 1986, the Golden State Killer launched a reign of terror and committed at least 5 rapes, 12 murders, and 120 residential burglaries throughout California. Then he disappeared without a trace.


Criminal DNA databases produced no hits, sweeps of crime scenes produced no fingerprints and despite very generous rewards, no one came forward with any helpful tips. Then former cold case investigator Paul Holes and genealogy expert Barbara Rae-Venter turned to familial DNA to help solve the case. has profiles of more than 16 million users and 23andMe has 10 million users. When you sign up to these websites, you receive a DNA testing kit to send a saliva sample off to the testing lab.

At the lab, your DNA sample enters the process of genetic sequencing, which involves cutting the DNA into tiny fragments and scattering them over a ‘genotyping chip’ to see what sticks. This will then identify the series of DNA letters in a sample, creating a genetic profile. Your genetic profile is then sent back to you.

Once your results arrive, you can upload your genetic profile to GEDMatch – a free online database where anyone can share their genetic profile if they wish. It’s a great way to research your family tree or discover if you have a genetic predisposition to any diseases.

This database is also used by law enforcement agencies to help solve serious and violent crimes. If law enforcement has biological material belonging to a person of interest from a crime scene – either old blood, hair or semen – they can search genetic profiles on GEDMatch to find a partial match also known as ‘Familial DNA’.

Familial DNA testing can only be used once the prosecution has proven all other reasonable methods of investigation have produced no results or that this is an emergency situation – for example, the serial killer is still a serious threat to the public.

Your DNA is roughly 50% similar to each of your parents, 25% for grandparents. First cousins share about 12.5% of their DNA, second cousins less than 4%, and third cousins less than 1%.

Investigators had knowledge of other basic information about the serial killer based on witness testimony. They suspected the serial killer is a white male approx. 5ft 10″ tall who lives or at least works in the California area.

A fake profile was then created using the serial killer’s DNA from a 1980 crime scene. This matched with a third cousin of the Golden State Killer.

Holes said five investigators spent four months building the family trees, generation by generation, name by name. They put this together using census records, newspaper obituaries, gravesite locaters, and police and commercial databases to find each relative.

His team then painstakingly created about 25 family trees containing thousands of relatives right from the killer’s great-great-great grandparents who lived in the early 1800s to the present day – the genetic profile of his third cousin.

They then found on one branch of this family tree a 72-year-old retiree named Joseph DeAngelo who was living quietly in the Sacramento suburbs. He matched a witness description – a white male standing 5′ 10″ tall and weighing 165-pound. He was also a former disgraced cop who had bought two guns during the time of the Golden State Killer’s activity.

via: Reddit

Next, they needed to obtain a new DNA sample from DeAngelo without his knowledge because the worst thing that could happen is he begins destroying a lot of crucial evidence. DeAngelo had a goldmine of overwhelming evidence against him including jewelry belonging to the victims.

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Police are legally allowed to collect “discarded DNA” without the suspect’s knowledge. We all shed DNA everywhere – we leave it on cups, straws, or on surfaces. This “discarded DNA” can only be used in evidence if left in a public place. If you discard a hairbrush in a trash can outside your house – that actually counts as a public place.

With DeAngelo placed under surveillance, investigators collected a new DNA sample using a swab of his car door handle.

On April 24th, 2018, Joseph DeAngelo was finally arrested. In June 2020, in a makeshift courtroom set up at Sacramento State University to allow for social distancing during the coronavirus pandemic – 74-year-old Joseph James DeAngelo Jr. uttered one word in his raspy, low voice – “guilty”.

So after 40 years of investigation, DeAngelo was finally caught because his third cousin sent a saliva sample to a genealogy website.


This is a potent weapon for police investigation and has closed many cold cases that would have otherwise remained unsolved. The Zodiac Killer could be caught using this exact same method.

Dr. Mark Perlin, chief executive officer and chief scientific officer of Pittsburgh-based Cybergenetics, explained: “DNA databases are an invaluable aid in solving cold cases, like stranger rapes and homicides. But so much more can be done to protect the public, just by using more of the information in the DNA evidence we already have.”

Michael Butterfield, writer and researcher for said,:

“The idea that Zodiac must be dead or in prison because we haven’t heard from him is wrong. I am somebody who subscribes to the idea that Zodiac is, in a sense, like DeAngelo. He was just leading in his life.

“I believe the case will be solved by the types of DNA evidence they have today. With that partial profile, with some renewed efforts that I’ve heard are going on, it’s possible they could get a complete profile and do what they did with the Golden State Killer.”

Controversy Surrounding Familial DNA

For more than 20 years, the ‘Grim Sleeper’ stalked women on the streets of South Central Los Angeles; killing at least 10 young African-American women between 1985 and 2007.

Late at night, the serial killer launched his vicious attack – smashing their heads with rocks or wrapping his hands around their neck. Sometimes he threatened them with a gun before raping and killing the victim then dumping the body in an alleyway.

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Local media called him ‘Grim Sleeper’ because he was dormant for 14 years before resuming his killing spree. Members of the local community complained that police were not taking the murders seriously. They believed this was because the victims were drug users and sex workers.

Finally, in 2010, DNA evidence tied Lonnie Franklin to those killings. He also became a suspect in multiple other murders with the real victim count believed to be approx. 100 women.

However, the DNA evidence that led investigators to Franklin wasn’t, in fact, his DNA – it belonged to his son after a 2008 arrest for firearm and drug offenses. In California, anyone arrested for a felony must give a DNA sample regardless if they are charged with the crime or not.

Police were then able to narrow down a list of relatives as suspects and eventually zeroed in on Franklin. However, authorities did not have a DNA sample for Franklin so they placed him under surveillance until they got one.

The suspected serial killer had a meal in a pizza diner and the leftovers, fork, and napkin were collected as evidence for DNA testing by a detective posing as a busboy. On June 6th, 2016, a Los Angeles County jury sentenced Franklin to death.

Tales of the Grim Sleeper (2014)

Since the case of the Grim Sleeper, familial DNA has helped to solve more than 28 cold cases. However, despite its clear benefits – familial DNA has caused a lot of controversies as it has been previously argued that the method invades privacy rights.

According to researchers at the University of California-Berkeley and New York University, familial DNA searching will often indicate that two people are close relatives when they are rather distant relatives. They found that cousins could be misidentified as siblings.

The report reads: “This type of mistake could cost investigators a lot of time and money, as well as intrude on innocent people’s lives and privacy. Investigators may be interrogating immediate family members who have nothing to do with the crime. Or, the familial search could implicate very distant relatives – so distant that their relationship with the suspects will not be helpful to investigators at all.”

African-Americans are disproportionately represented in criminal databases. The researchers found in this experiment, “while the overall rate of false identification of unrelated individuals remains low,” the rate of false positives of African Americans was “much higher, roughly two orders of magnitude higher” than other groups.

Which will lead to African Americans suffering disproportionately from intrusions of privacy and police interrogations. GEDMatch has since updated their terms of service to inform users that law enforcement is using the database to solve crimes. Which is perfectly legal, for now.

This won’t be the last time we see familial DNA being used to solve cold cases or we hear of the controversy that surrounds it.