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DNA testing helps lead to arrest in 5-year-old murder case in Tooele

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Posted at 9:55 PM, May 09, 2016
and last updated 2016-05-09 23:55:49-04

SALT LAKE CITY, Utah – Familial DNA testing is what helped Tooele police find a suspect in a five-year-old murder case. It’s one of two tests the state crime lab has done since it started the program in 2014.

State crime lab director Jay Henry said the use of familial DNA testing has been around for about 10 years, first developed in the United Kingdom, but has become more wide-spread.

It works by taking an unknown DNA sample and comparing it to samples in the Utah offender database. The test looks at 13 specific markers that would indicate blood relation.

“Typically you’re looking for… do they have siblings, do they have children, do they have parents, in that male line who could be a possible suspect,” Henry said.

Tooele Police announced last week familial testing led them to Rojelio Diaz Jr., the suspect in the 2011 murder of 69-year-old Evelynne Derricott.

A DNA sample from the murder weapon matched to relatives of Diaz already in the state database, detectives then use their own legwork to track Diaz down.

“You have to actually find who the family member is,” said Tooele County Chief Deputy Attorney Gary Searle. “We don’t go out and just get DNA samples from 15 different people, that would be a violation obviously, we think of someone’s privacy.”

The test is only as accurate as the database itself. Henry said there are approximately 110,000 samples in the Utah database, but an estimated 46 percent of current inmates have a relative in the CODIS system.

“The technology is continually changing,” Henry said. “That’s why we’re starting to see some of these other successes there.”

The current crime lab policy puts familial testing as a last resort, only done after all other efforts have failed. It requires a lot of time and resources, and costs upwards of $5,000.