The Swedish students who tackled Brock Turner break their silence

WARNING: Distressing details.

One of the two Swedish heroes who caught Brock Turner sexually assaulting an unconscious woman behind a dumpster at California's Stanford University last year has broken his silence.

Carl-Fredrik Arndt and Peter Jonsson were cycling to a party on January 18, 2015 when they saw Turner on top of the victim. The PhD students tackled the swimmer, then aged 19, before holding him down and calling police.

"We saw that she was not moving, while he was moving a lot," Arndt told Sweden's Expressen, as reported by BuzzFeed News. "So we stopped and thought, 'This is very strange'."

Arndt said he and Jonsson approached Turner to find out what was going on.

"When he got up we saw that she still wasn't moving at all, so we walked up and asked something like, 'What are you doing?'" he said.

Turner fled, but Jonsson caught him and pinned him to the ground.

Arndt remembered leaning over to make sure the half-nude victim was still alive. "She lay perfectly still," he said.

Arndt and Jonsson later told authorities they saw Turner on top of the victim "aggressively thrusting his hips into her."

"She was unconscious. The entire time. I checked her and she didn't move at all," Arndt said, according to CBS News.

"The guy stood up then we saw she wasn't moving still. So we called him out on it. And the guy ran away, my friend Peter chased after him."

Police said Jonsson "became very upset, to the point where he began crying while recounting the incident ... he said it was a very disturbing event for him to witness and be involved in."

Peter Jonsson and Carl-Fredrik Arndt caught Brock Turner assaulting an unconscious woman behind a dumpster at California's Stanford University. Photo / LinkedIn/Facebook

The victim, who has not been identified, described in her powerful impact statement the condition in which Turner left her.

"I learned that my ass and vagina were completely exposed outside, my breasts had been groped, fingers had been jabbed inside me along with pine needles and debris," she wrote.

The victim, now aged 22, also wrote in her 7000-word letter that she would be forever grateful to Arndt and Jonsson.

"Thank you to the two men who saved me, who I have yet to meet," she wrote.

"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."

While Jonsson has not given an interview, he shared the victim's statement on his Facebook page and thanked supporters.

"Thanks to everyone, friends and strangers, for all the encouragement and support over the last days and months. At this point I will not publicly comment on the process or the outcome of the trial," he wrote.

"I do ask all of you to spare a few minutes and read this letter written by the victim. 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."

Buzzfeed reports Arndt worked as a maths and engineering teaching assistant while getting his degree at Stanford, while Jonsson received his Master of Science degree in Management Science and Engineering from the university in May.

This January 2015 booking photo released by the Santa Clara County Sheriff's Office shows Brock Turner. Photo / AP

Arndt and Jonsson have been hailed as heroes for stepping in to help the victim.

"I can't understate how important those two heroes were in this case," Santa Clara County Deputy District Attorney Alaleh Kianerci told Huffington Post.

Had they not intervened, "we wouldn't know who the perpetrator was," and the case would not have been "a prosecutable one" as the victim was unconscious, he said.

Turner, a former Stanford University student, was found guilty of three counts of sexual assault in March. He faced a maximum of 14 years in state prison, but on Thursday was sentenced to just six months in jail and probation.

Santa Clara County Superior Court Judge Aaron Persky has come under fire for the lenient sentence, with more than 371,000 people signing a petition calling for him to "be removed from his judicial position."

It has been revealed Judge Persky was a Stanford University graduate and was captain of the lacrosse team.

After the sentencing, Local District Attorney Jeff Rosen said: "The punishment does not fit the crime. The sentence does not factor in the true seriousness of this sexual assault, or the victim's ongoing trauma. Campus rape is no different than off-campus rape. Rape is rape."

Turner's father, Dan Turner, issued a tone-deaf statement defending his son.

"He will never be his happy go lucky self with that easy going personality and welcoming smile," he wrote.

"His every waking minute is consumed with worry, anxiety, fear and depression. Now he barely consumes any food and eats only to exist. These verdicts have broken and shattered him and our family in so many ways. His life will never be the one that he dreamt about and worked so hard to achieve. That is a steep price to pay for 20 minutes of action out of his 20 plus years of life."

The shocking case has received widespread attention around the world, with many people arguing the light sentence proves the legal system often favours perpetrators over victims.