MADISON, Wis. -

The image on the computer screen speaks in a cold and matter of fact manner about acts difficult to comprehend. He is a 17-year-old boy talking with police investigators about his plan to abduct, murder, rape and dismember a 10-year-old girl. Madison psychologist Anna Salter’s challenge is to make some sense out of a completely senseless act.

“I was befuddled. How could any human being do this kind of thing?” Salter said.

Salter is an expert in the analysis of sexually violent and sadistic criminals. She has provided analysis for prosecutions on some of the most high profile cases in the country. When investigators and prosecutors in Jefferson County, Colo., started looking for answers in the death of Jessica Ridgeway, they turned to Salter.

“I think there’s a human, natural, human instinct to reach for the why, to search for an explanation,” said Hal Sargent, chief deputy district attorney in Jefferson County, Colo.

Ridgeway, a 10-year-old girl, disappeared on the morning of Oct. 5, 2012, shortly after leaving for school. Her disappearance sparked a massive search by law enforcement and community volunteers. That search ended when her body was discovered in a field miles from her home.

DNA evidence was recovered by investigators. Fearing his arrest was imminent, 17-year-old Austin Sigg called police and turned himself in.

“That night he was willing to talk to police, and he talked to them for six hours,” Salter said.

During that interrogation, Sigg confessed to investigators. He spoke at length about the killing and about a failed attempted abduction he was involved in prior to the Ridgeway case.

“He talked in matter-of-fact about killing her as he would have about going to the grocery store,” Salter said.

Salter’s mission was to sift through a massive amount of information about Sigg and his family to find some answer about who he had become and why. That information would be important in the sentencing of Sigg.

“I received school records and all kinds of information they had in the case. It was an overwhelming amount,” Salter said.

She spent days pouring over the information, interviews and interrogation tapes. What she found was a killer who gave very few clues about what he planned to do.

“Mostly there weren’t any red flags for neighbors. The only thing that was odd about him is how many high school students drop out of school to go into mortuary school?” Salter said. “He had an interest in dead bodies.”

“The problem with sadists is they’re often very, very competent and adult sadists, many of them are middle class, and one study showed 65 percent of them had no criminal record,” Salter said. “This kind of offender is different. This kind of offender is living a double life and is competent and capable of acting normally when he is in public or when he is with his family.”

Salter testified for the prosecution at Sigg’s sentencing hearing. She told the judge there was no evidence Sigg had been abused or neglected as a child. Her assessment of Sigg was he exhibited sadistic and narcissistic behavior.

Sigg was sentenced to life in prison plus 86 years.

Doing the work Salter does is not easy. While providing an assessment of Sigg, Salter was also doing analysis on two other homicide cases involving torture. She testified in all three cases over a span of three weeks. Spending days and weeks looking into the darkest corners of minds of killers is difficult.

“I had three cases in a row where children were tortured, and by the end of it if I needed a retreat. I had to stop because I don’t care how professional you are or how much research you read or how much distance you try to put between yourself and this kind of case, if you are a human this kind of case is going to affect you,” Salter said.

She said even though her work takes a toll on her emotions, it is work she remains committed to. Her work gives guidance to prosecutors and helps to keep communities safe from the Austin Siggs of the world and one day may provide the illusive answer to the question, why?

“What other hope is there except that we can make enough sense of it to begin to develop some kind of way to prevent it?” Salter said.