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1988 cold case solved using DNA by San Diego County Sheriff's Dept.

Posted at 5:02 PM, Mar 16, 2022
and last updated 2022-03-16 21:19:54-04

SAN DIEGO, Calif. (KGTV) - The San Diego County Sheriff’s Department has solved a decades-old cold case thanks to DNA.

May 2, 1988, Diane Dahn was found dead in her Santee home with stab wounds to her chest. Her two-year-old son was found wandering their complex. At the time, detectives were not able to figure out who killed her.

There have been multiple attempts to solve the crime throughout the last few decades. In 2000, fingernail DNA was taken but no matches were found. In 2010, a single hair that had been found in Diane’s hand was processed, but there were no matches, although it matched the fingernail DNA from 2000. It wasn’t until 2020 that the cold case team used investigative genetic genealogy to solve the crime.

The investigators had the DNA profile from the hair, then matched it with other DNA profiles that had been entered into a database.

“In the end, nine trees were constructed with almost 1,300 individuals connected to the suspect via either marriage or blood,” said Senior Crime Intelligence Analyst Jeff Vandersip.

All of the people matched had some connection to the suspect, but investigators had to figure out what the connections were. After a year and a half of digging, they determined a man named Warren Robertson matched the DNA of the suspect. Robertson was one of Diane's neighbors at the time and was killed in a house fire in 1999, but Diane’s sister said the information still brings her family peace.

“I didn't think anything was ever going to come of this, I thought I myself was going to go to my grave not knowing,” said sister Victoria Dahn-Minter.

This is the fifth cold case the San Diego County Sheriff’s Department has solved using Investigative Genetic Genealogy. Investigators said now that the technology is more advanced, they hope to continue to solve the hundreds of cold cases in their system.

Investigators said a key tool in solving these crimes is having more people’s DNA entered into their system.

“Because the more people that put their DNA in these systems, the better chance we have of solving a case,” said Brian Patterson.

Patterson said they only analyze people who voluntarily share their DNA with two different companies. If people would like to help solve cold cases by sharing their DNA with authorities, they can go through either FamilyTreeDNA or GEDMatch.