Key Witness in Stanford Sexual Assault Case Speaks Out

It's been almost a year and a half since Stanford University swimmer Brock Turner sexually assaulted a woman on the California campus and a key witness in the case is now speaking out.

In an interview with ABC News, Swedish doctoral student Carl-Fredrik Arndt said he and his friend Peter Jonsson were riding their bikes through campus in January 2015 when they spotted Turner on top of a woman behind a dumpster outside a fraternity house. Jonsson immediately sensed something wasn't right, Arndt said.

"She wasn't moving," he told ABC News during an interview in Palo Alto, California, on Tuesday night. "She was half-naked."

The two Swedes decided to intervene. Jonsson shouted at Turner, "What the f--- are you doing?"

There was an exchange of words, and then Turner fled as the two men approached, Arndt recalled.

Jonsson chased down Turner while Arndt stayed with the victim. Arndt said the woman was unconscious the entire time and he checked "to make sure she was still alive."

"I was quite in shock for quite a long time - both me and Peter," he told ABC News. "It's still hard to think about."

Arndt said he and Jonsson restrained Turner, then a Stanford freshman, as they called police and waited until officers arrived. The two graduate students testified in court.

Turner, 20, was convicted in the attack and sentenced to six months in jail and three years of probation by Judge Aaron Persky last week. But he's expected to be released three months early, on September 2. A jury found him guilty in March of three felonies: assault with intent to commit rape of an intoxicated/unconscious person, penetration of an intoxicated person and penetration of an unconscious person. The verdict has sparked national outrage from critics who questioned why the former Stanford student received little jail time. Arndt said he wouldn't comment publicly on the proceedings or outcome of the trial. Turner plans to appeal his conviction.

Stanford University issued a statement Monday, calling it a "horrible incident" but defending how it handled the aftermath, saying it "did everything within its power to assure that justice was served."

"Once Stanford learned the identity of the young woman involved, the university reached out confidentially to offer her support and to tell her the steps we were taking," the university said. "In less than two weeks after the incident, Stanford had conducted an investigation and banned Turner from setting foot on campus - as a student or otherwise. This is the harshest sanction that a university can impose on a student."

Arndt said neither he nor Jonsson has seen the victim since the incident.

Still shocked by what happened, Arndt said he's unsure what he would say to the woman if he saw her again.

"It'd be hard," he told ABC News. "It'd be hard to know what to say."

In court, the unidentified victim read a statement to the judge that directly addressed her attacker and also thanked the two Swedes. Her letter went viral after she gave it to the media.

"Most importantly, thank you to the two men who saved me, who I have yet to meet," her letter reads. "I sleep with two bicycles that I drew taped above my bed to remind myself there are heroes in this story. That we are looking out for one another. To have known all of these people, to have felt their protection and love, is something I will never forget."

In a Facebook post on Tuesday, Jonsson shared a link to the letter, published by Buzzfeed, and wrote, "To me it is unique in its form and comes as close as you can possibly get to putting words on an experience that words cannot describe."