In January 2015, Swedish PhD students Carl-Fredrik Arndt and Peter Jonsson were cycling to a party at Stanford University when they saw champion swimmer Brock Turner lying on top of a woman behind a rubbish skip bin.
Carl-Fredrik Arndt (Facebook) and Peter Jonsson (Linkedin)
They say they immediately knew something was wrong.
"We saw that she was not moving, while he was moving a lot," Mr Arndt said to the Swedish news outlet Expressen. "So we stopped and thought, 'This is very strange.'"
They approached Turner, 20, to see what was happening.
"When he got up we saw that she still wasn't moving at all, so we walked up and asked something like, 'what the hell are you doing?'"
Turner ran away, but Mr Jonsson chased after Turner and tackled him.
Mr Arndt checked to make sure the unconscious victim was still alive, as "she lay perfectly still".
They then held Turner until police arrived.
This week Turner was convicted of three counts of sexual assault, and sentenced to three months of a six-month sentence in county jail with probation.
In a courtroom letter, the victim said she was told one of the two Swedes was crying because he was so distressed by her condition when he found her. She said she would always be grateful to Mr Arndt and Mr Jonsson for helping her.
"Thank you to the two men who saved me, who I have yet to meet," the victim 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."
On Tuesday, Mr Jonsson posted the letter to his Facebook page, thanking "everyone, friends and strangers, for all the encouragement and support over the last days and months."
He would not publicly comment on the process or the outcome of the trial, but asked everyone to read the letter.
"To me it is unique in its form," he wrote, "and comes as close as you can possibly get to putting words on an experience that words cannot describe."