Detectives say Vierstra and the victim attended a party on the 700 block of Nez Perce Drive. Vierstra and the victim, a current U of I student, agreed to leave the party and go for a walk. Police said the two began kissing before he forced her to the ground and sexually assaulted her behind the Sigma Chi fraternity house.
Moscow Police Chief David Duke said Vierstra was a former U of I student and knew the victim from the Twin Falls area.
"The victim knew the suspect from working with him in Twin Falls at a restaurant, so they were acquainted, but on a friendship level only," said Duke.
The victim told her family about what happened and they contacted police early Sunday morning. After talking with the victim and others, police contacted Vierstra and took him into custody.