A simple hand-drawn picture of two bicycles has been taped above the bed of a 23-year-old woman to remind her, she says, that there are "heroes in this story".

It's a narrative containing truly appalling and harrowing details: of the unconscious woman being raped behind a bin on the Stanford University campus in the US; of waking in hospital to learn of her assault; of watching as her attacker Brock Allen Turner, a champion swimmer with Olympic ambitions, escape with a six-month sentence decried by critics as far too lenient.

Those bicycles above the woman's bed are a small reminder of two university students, whom she did not know, and who were cycling by the dark alley when they saw something amiss and stopped to intervene.

For the first time, one of those "hero" post-graduate students - Swedish nationals Carl-Fredrik Arndt and Peter Jonsson - has spoken of the night in January last year when, as they were cycling to a party, they saw from a distance the figures of a man and a woman behind a bin. They approached and knew something was terribly wrong.

"She was unconscious the entire time. I checked her and she didn't move at all," Mr Arndt told CBS News this week.

Mr Arndt, who was studying for a PhD in computational and mathematical engineering at Stanford University at the time, told Swedish newspaper Expressen that he and his friend confronted Turner, then 19, demanding to know:  "What the hell are you doing?"

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

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

Mr Arndt said Mr Jonsson, who was studying for a master's degree in management science and engineering at Stanford, chased and tackled Turner about 30 metres from the bin. He held him until the police arrived a short time later.

In a powerful victim impact statement delivered to the court, and which has since been shared widely on social media, the unnamed woman praised the university students for saving her.

"Most importantly, thank you to the two men who saved me, who I have yet to meet," she said in her 7000-word statement.

"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."

The woman said she was terrified by the thought of how the night could have ended if the students had not intervened.

"I don't sleep when I think about the way it could have gone if the Swedes had never come," the woman said.

"What would have happened to me? That's what you'll never have a good answer for, that's what you can't explain even after a year."

Mr Arndt told Expressen that he had still not met the woman, but had read her "very strong" victim impact statement.

"Obviously, it is a great joy to be able to help her," he said.

Mr Jonsson has not spoken publicly about the incident, but posted a message on Facebook thanking "everyone, friends and strangers, for all the encouragement and support over the last days and months", Heavy reported.

"At this point I will not publicly comment on the process or the outcome of the trial," he wrote on Facebook on Tuesday.

"However, 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."

Turner, who was convicted of three felony sexual assault charges in March, faced up to 14 years in jail when he appeared in court late last week for sentencing. Prosecutors asked for a six-year jail term.

But instead, Santa Clara County Superior Court judge Aaron Persky sentenced Turner to only six months in jail and three years of probation. He said a longer sentence would have a "severe impact" on Turner, now 20.

Turner's father complained that his son's life had been ruined for "20 minutes of action" fuelled by alcohol and promiscuity, comments that ignited public outrage.

smh.com.au