Local News

SBI crime lab tackles digital evidence

Posted July 16, 2010 6:08 p.m. EDT
Updated July 16, 2010 7:52 p.m. EDT

— There was a time when criminals did their business on street corners or back alleys. Today, things happen in a new virtual world, and law enforcement must keep pace to solve crimes.

That's where the State Bureau of Investigation Crime Lab's Digital Evidence Unit comes into play.

The unit's six analysts and three technicians use sophisticated software and hardware to sift through vast information stored on computers, cell phones and other electronic devices to gather evidence to help solve crimes, such as homicides, rapes, bomb threats and others.

About 70 percent of the cases the unit investigate, involve crimes against children, such as child abuse, pornography and Internet solicitation.

"We use special tools and techniques to see things that don't appear to the user as they're sitting at the computer," said SBI special agent John Dilday, who heads the digital evidence unit. "It's sort of like an autopsy."

Analysts typically disassemble computers or other devices to remove their hard drives and then make what's called a forensic image.

In 2003, the body of Janine Sutphen, a 57-year-old cellist with the Durham Symphony, was found in Falls Lake. Her husband, Robert Petrick, was convicted of her murder after investigators found key evidence on his computer.

"On one of his computers, we found it had been used to search for local lake levels, lake access and underwater topography of lakes, including Falls Lake," Dilday said.

Dilday and his team emphasize that, for digital evidence to hold up in court, they must prove that the original data wasn't altered.

"We don't want to make any changes to the original drive at all," he said.

The digital analysts also clean up audio files by filtering out background noise and enhance surveillance videos by capturing still images of suspects. That played a key role in capturing the suspects in the death of Eve Carson, the student body president at the University of North Carolina in Chapel Hill, who was shot to death in March 2008.

"We get still photos from the videos and get them back quickly to investigators so they can distribute the photos to the media and fellow law enforcement (agencies) to put out a dragnet, if you will, to capture the suspect as soon as possible," Dilday said.