(CBS SF) — One of the witnesses who interrupted the sexual assault by a former Stanford swimming star – who avoided a prison sentence and received a six-month jail term – has come forward to describe what he saw.

The unidentified victim’s letter to the judge describing the emotional impact of the crime has reached a worldwide audience and drawn new focus on the issue of campus sexual assault.

Brock Turner was on top of the unconscious woman on the ground outside a fraternity party just before 1:00 a.m. on January 18th when two graduate students on bicycles, Carl-Fredrik Arndt and Peter Lars Jonsson, noticed them and went to investigate, according to court documents.

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Turner saw them, got up off the woman and began to run away. After checking on the woman, they saw that she was unconscious but breathing.

“She was unconscious. The entire time. I checked her and she didn’t move at all,” Carl-Fredrik Arndt told CBS News.

Arndt and Jonsson told police they saw Turner on top of the victim “aggressively thrusting his hips into her.”

“The guy stood up, and 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,” Arndt told CBS News.

Both Arndt and Jonsson struggled with Turner and restrained him officers arrived, court documents said.

Turner’s six month sentence, in which he will likely only serve three months, has generated outrage worldwide along with a petition to remove Santa Clara County Judge Aaron Persky from his post.

Turner’s father, Dan Turner, has also created an uproar over his statement to Persky ahead of sentencing, in which he said “His life will never be the one that he dreamed 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.”