Stanford rapist Brock Turner blamed alcohol and “party culture” for his sex assault against an unconscious woman — but a witness who intervened said the former star swimmer seemed in control of himself.

Graduate student Carl-Fredrik Arndt was riding bicycles with a friend when they encountered Turner, then 19, sexually assaulting the 23-year-old woman outside a fraternity party in January 2015.

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Arndt described the encounter Thursday night to Greta Van Susteren on Fox News, saying he and his friend noticed something was wrong because the woman wasn’t moving.

He and his friend, Peter Jonsson, intervened and “called the guy out,” and he said Turner fled after briefly talking to them.

Jonsson chased after Turner, and both men restrained the rapist until police arrived.

Van Susteren asked whether Turner seemed drunk, and Arndt simply said: “No.”

“He could run, so I guess that answers the question,” he added. “He could speak without slurring at all.”

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The 23-year-old victim admitted drinking too much at the party, and her blood-alcohol level was three times the legal limit after the attack.

Turner’s blood-alcohol level was twice the legal limit, but he told investigators he could recall everything that happened that night.

Arndt said the woman, who had gone to the party with her younger sister, remained unconscious even after the two friends intervened.

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“She was never moving,” he said. “Like you can read in the court statement, she had a dress but it was pulled up.”

Turner testified during his trial that the woman told him she could touch her genitals, but Arndt said the woman was clearly unconscious when he and Jonsson came upon them.

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He said Turner never offered an explanation for his actions with the unconscious woman, and Arndt declined to offer details about what the assailant said before running away.

Arndt and Jonsson had another bystander call police after more people came to the scene.

He declined to comment on the six-month sentence Judge Aaron Persky gave to Turner, who was convicted

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“It was a horrible thing to experience — obviously it would be for anyone,” Arndt said. “It was very shocking and disturbing at first. It’s something I’ve thought a lot about and I’ll bear with me for a very long time. Not in the same way they will, but it’s still something that’s horrible to experience.”

Van Susteren grew frustrated by Arndt’s refusal to comment on so many aspects of the incident, and she asked him why he had even agreed to the interview.

I think it’s an important issue, and it seems like people appreciate it when it comes out, and it seems like it’s a big problem, in general, in the U.S.,” Arndt said. “I don’t want to make personal statements about it because I don’t think that’s up to me, but I still think this issue is clearly worth highlighting.”

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