Brendt Christensen U of I case turns on the footprint of a killer

In a murder case with no body and no fingerprints, there are footprints.

Digital footprints. And lots of them.

Ex-University of Illinois grad student Brendt Christensen was an avid researcher of torture techniques, perversion, murder and human disposal according to a federal agent who testified today at Christensen's trial in downstate Peoria.

Attorneys for Christensen, 28, have already admitted in open court that he kidnapped and killed U of I scholar Yingying Zhang two years ago. The body of the Chinese national has never been found and Christensen is being tried in federal court where a jury could deliver him a death sentence.

During their investigation of Christensen, authorities discovered what amounts to a digital roadmap of his plans and plots, said

senior FBI forensic examiner William O'Sullivan with the Springfield field office.

On the confessed killer's computer, Sullivan said that agents found he had a profile on a website called "Fetlife"...as in fetish.

He described it as "the Facebook for kinky people." Christensen's computer had hidden files displaying photos of woman bound, gagged and being assaulted.

In one post on the site found by the FBI Christensen wrote to another Fetlife user: "I'd bind you, gag you, and likely put you in a duffel bag so no one could see you."

It may be no coincidence that Christensen actually bought a 6-foot long "super tough heavyweight" duffle bag on Amazon just days before he kidnapped Zhang. That oversized duffle bag has never been found.

Investigators say they also determined that Christensen frequented a forum titled "Abduction 101: Questions and answers."

They also traced some of his reading material before and after Zhang vanished. It included an article on serial killers and another entitled "Beyond the Grave: Understanding Human Decomposition" which featured photos of human remains.

Also on Monday, ABC7 is showing the first video interview the FBI did with Christensen in their offices in June 2017.

The video answers, the descriptions of what Christensen was perusing on his personal computer and the Fetlife data all suggest that federal agents were pursuing a man obsessed with controlling women-and they say, in Zhang's case, killing her.

Christensen also researched serial killers-and one in particular, David Parker Ray.

He was known as the "Toy Box Killer," the name given for his soundproof trailer in the New Mexico desert where investigators suspect he abducted, tortured and killed more than 50 women. In 2002 Ray died of a heart attack in prison at age 62.

In Christensen's case, the government wants him to die at their hands. A death penalty proceeding would follow a guilty verdict in Peoria federal court.