One of the two Swedish Ph.D. students who served as key witnesses at the trial of Stanford University student Brock Turner, who sexually assaulted an unconscious woman behind a dumpster in January 2015, has opened up about the incident.

On January 18, 2015, Carl-Fredrik Arndt and Peter Jonsson were biking around campus in Palo Alto, California on their way to a party when they came across what they initially thought was an “innocent hook up.”

However, when they saw that the woman was not moving, they sensed that something was wrong. They approached Turner, a member of the swim team, and found out that he was raping her.

“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?’” Arndt said in an interview with Expressen, a news outlet in Sweden.

Arndt and Jonsson spoke with Turner briefly before he got scared and attempted to run off. However, Jonsson was quick to catch up to him. He tackled him to the ground and restrained him while Arndt stayed with the victim to make sure she was alright.

The two then called 911 and with the help of two other men, they held on to Turner to keep him from escaping until the police arrived and arrested him.

In a police report that was filed after the attack, Jonsson was described as being “very upset, to the point where he began crying while recounting the incident” and giving his statement.

“He said it was a very disturbing event for him to witness and be involved in but he just reacted to the situation at hand without really thinking,” the officer said, according to the Daily Mail.

Turner was found guilty of three counts of sexual assault back in March. However, controversy arose when Judge Aaron Persky gave him a lenient sentence last week, sentencing him to just six months of prison time and three-month probation.

Meanwhile, the victim, who is now 23-years-old and was not named, wrote a letter and allowed it to be read in court.

In it, she thanked both Arndt and Jonsson for saving her from further harm, criticized Turner for denying he had done anything wrong, and expressed her disappointment at the “gentle” sentence that he was given.