SAN FRANCISCO (AP) — Northern California detectives still trying to identify the infamous Zodiac Killer who targeted victims in the late 1960s and taunted investigators with letters say they hope to try the same DNA tracing technology recently used to arrest a suspect in another string of cold-case serial slayings — those blamed on the Golden State Killer.

But first they have to get a better DNA profile.

Several months ago, the Vallejo Police Department sent two letters written by the Zodiac Killer to a private lab in hopes of finding his DNA on the back of the stamps or envelope flaps he may have licked. They are expecting results soon.

“They were confident they would be able to get something off it,” Vallejo police Detective Terry Poyser told the Sacramento Bee.

Poyser said he hopes a full DNA profile will be found that will let detectives try the same DNA sleuthing techniques that investigators used to arrest Joseph DeAngelo on April 25. Authorities suspect he committed at least a 12 murders and 50 rapes in California between 1976 and 1986.

Investigators uploaded DNA collected at one of the crime scenes to an open-source genealogical website and found a partial match to a distant relative of DeAngelo’s. From there, they painstakingly constructed a family tree dating back several generations before they zeroed in on DeAngelo.

Some privacy advocates say they are concerned with the process and worry about future abuses, but detectives investigating the Zodiac Killer say they hope the technique will help solve one of the most vexing cold cases in the country.

“That’s a great idea,” said Gary Harmor, founder and director of the Serological Research Institute, a private DNA lab. “I think we’ll see more investigations use this technique.”

Detectives in Southern California are testing DNA collected from a double murder and rape to see if they can be tied to DeAngelo. Another man, Craig Coley, was recently cleared of those crimes after spending 38 years in prison in the murder of a 24-year-old college student and her 4-year-old son in 1978.

The Zodiac Killer fatally stabbed or shot to death five people in Northern California in 1968 and 1969, and their killer sent taunting letters and cryptograms to the police and newspapers. The Vallejo police became the lead investigators because the first two victims were killed there.

He was dubbed the Zodiac Killer because some of his cryptograms included astrological symbols and references.

Various pieces of evidence, including a rope used to tie a victim as well as the letters, have been tested unsuccessfully for the killer’s DNA profile. Poyser said recent advances in DNA testing prompted investigators to seek a match on two of the killer’s letters.

“We actually sent these samples in a few months ago, just as a matter of due diligence in the case,” Vallejo Mayor Bob Sampayan told the San Francisco Chronicle.

Sampayan, a former Vallejo police homicide investigator, said, “It’s the right thing to do. The database gets larger and larger every year, and technology improves, so there is always a possibility of something coming up.”

The 2007 movie “Zodiac,” starring Jake Gyllenhaal and Robert Downey Jr., renewed widespread interest in a case that has always had a cult following of amateur detectives and cryptographers who sought to crack the killer’s code.

One of those amateur sleuths, Tom Voigt, said the key to solving the Zodiac killings is mimicking the Golden State Killer investigation, which included forming a full-time task force dedicated to the case and exploiting publicly accessible DNA databases.

Voigt said the Zodiac case was being investigated part time by a Police Department in a city that filed for municipal bankruptcy.

“There’s a formula to follow,” Voigt said. “And it’s to simply copy what happened to the Golden State Killer.”

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Information from: The Sacramento Bee, http://www.sacbee.com