Drawing on innocent victim's darkest memories, a local woman tells FOX40 how she helps shed light on some of Sacramento's most horrific crimes.

"They have to re-live through the crime again. They have to put themselves back in there," Joyce Ly said.

Ly is the Supervising Forensic Identification Specialist with the Sacramento County Sheriff's Department. When she's not examining fingerprints, she's creating composite sketches of accused criminals.

"I have the easy part of sitting behind the sketchpad to sketch, and it's really the eyewitness and the victim who has the difficult part of trying to recall all the features," Ly said.

While others in her field choose to use computer programs, Ly prefers to hand draw her sketches for accuracy.

"With the stroke of a pencil or an eraser I can easily make changes," Ly said.

But the process isn't as simple as it may sound. Ly often goes to crime scenes where people have recently been victimized. As you can imagine, getting descriptions from someone in a heightened emotional state requires delicacy.

"I can't break down and cry, but I definitely empathize with them," Ly said.

Once Ly makes sure the victim she is working with is as comfortable as possible, she asks them to think about the suspect's face, take a snapshot in their mind, and describe it to her.

"I usually start with the head. The shape of the head is very important. If you get that wrong it can throw everything off," Ly said.

Once Ly has a rough sketch of all the facial features, she has the victim flip through a facial recognition book provided by the FBI. It contains thousands of different facial features and expressions.

The adjustment process can take several hours.

Most recently, Ly's sketches have identified two young men separately accused of forcing two older women into their homes and sexually assaulting them. Their mugshots are unavailable as they are currently awaiting trial, but sources tell us they are spot on.

However, recently, another suspect Ly sketched, 30-year-old David Oliver Dixon, was convicted of assault with a deadly weapon and sentenced to 13 years in state prison.

In April of 2014 an American River College student was walking on the Arcade Creek nature trail just 200 yards from campus when she said a man with a knife assaulted her. She said he grabbed her arm and told her to be quiet, but she screamed and got away. And remarkably, during that brief encounter, she was able to remember enough information about what he looked like to come up with a sketch.

Ly's sketch helped bring Dixon into custody. At the time, he was already on California's sex offender registry, previously convicted of assault with intent to commit a sex crime.

"He stopped the police car and said there had been somebody attacked back here, and so we needed to be really careful," Cindy Russell said.

Russell tells FOX40 she was on the Arcade Creek trail behind American River College the day that student was assaulted. She said if she were the victim, she didn't know if she would be able to recount so many details about the suspects face.

"So what she did was amazing," Russell said.

She's since heeded warning signs on the trail, taking out her earbuds and paying attention to her surroundings, even though she shouldn't have to.

"I don't understand the society that's become so violent and so angry," Russell said.

Luckily Ly doesn't have to understand what makes criminals tick to help track them down.

She just has to understand what their victims see.

"The human mind is an amazing thing. Just a split second, and they're still able to recall details and features to come up with a sketch that's accurate, that look like the suspect," Ly said.

Video: http://fox40.com/2015/11/02/the-unse...sed-criminals/