After a lengthy investigation, Pullman police say a Washington State University student raped an 18-year-old woman who had passed out during a party at an off-campus fraternity house.

The woman told police she was provided alcohol and raped on the night of Sept. 2, 2016, in the basement recreation room of the Delta Upsilon house, 815 N.E. Ruby St. The fraternity was disbanded weeks later after three other women said they believed they had been drugged while drinking at the house.

Pullman police Cmdr. Chris Tennant confirmed the department recently sent its findings to the Whitman County Prosecutor’s Office and requested a second-degree rape charge against a 20-year-old suspect, a development first reported by Pullman Radio News.

“We have what we believe is probable cause,” Tennant said. “Of course, the prosecutor’s office has a different standard for that, and we’ll find out soon if they’ll file charges.”

Tennant declined to name the suspect because he has not been charged or arrested. He said the suspect had been a member of Delta Upsilon and was enrolled at WSU as recently as last semester.

The investigation was led by Detective Heidi Lambley and involved biological evidence, several search warrants, and interviews with the victim, suspect and others who were at the party. Tennant said investigators also reviewed surveillance video that corroborated other pieces of evidence but did not capture the rape itself.

Asked about the length of the investigation, Tennant said it’s “not unusual” for Pullman police detectives “to follow cases to their logical conclusion.”

“What’s unusual in this case is that we have so much information,” he said. “These are very, very difficult crimes to investigate, in general, because usually there are no witnesses and physical evidence is hard to get a hold of.”

Second-degree rape is a felony. An employee at the prosecutor’s office said there’s no fixed timeline on charging decisions.

Police did not find enough evidence to support the drugging allegations. Tennant has previously said that common “date rape” drugs leave the body quickly, making it difficult to prove that someone was drugged.

After the Delta Upsilon house was shuttered, WSU said the fraternity would be ineligible for university recognition until 2021. It was not the first or last WSU Greek house to face such a suspension.

Months earlier, in April 2016, WSU’s Interfraternity Council reported that a new member of Phi Delta Theta had suffered life-threatening alcohol poisoning after the fraternity held “a competition in which members were separated into teams based on their pledge class years, and were challenged to consume as much hard alcohol as possible.”

In November 2016, the IFC and the Panhellenic Council, both student-run organizations, imposed a semesterlong ban on football tailgates, “21 runs,” “date dashes” and other social events where alcohol would be consumed.

Student leaders at the University of Idaho followed suit last month, saying the hope is to combat a “growing national crisis” of binge drinking, hazing and sexual violence on college campuses.