The officers expected the revelers to flee when they arrived at a house party in a small central Washington town, where they say a dozen young people overdosed on an unknown substance.

But they didn't expect the chaos they found inside after kicking down the door because no one responded, police said. Unconscious and semi-unconscious partygoers were scattered throughout the home, and one man was found engaging in a sexual act with a semiconscious female, who was later determined to be his girlfriend, police said.

"The house was packed with people. We found people passed out, incoherent, of all different levels of intoxication ... (some) in need of medical attention" Cle Elum Sgt. Monty Moore said. "There was vomit everywhere, inside and out."

In the basement, some of those who were sober had tried to help others by putting them on beds, couches or mattresses.

"However, not one person chose to call 911," Cle Elum Police Chief Scott Ferguson said.

Officers and Kittitas County sheriff's deputies went to the home in downtown Roslyn, about 80 miles southeast of Seattle, late Friday after receiving a report of a possible overdose victim at a nearby grocery store. The victims' friends told officers about the party.

As many as 50 underage people were at the party, most of them Central Washington University students between 18 and 21. Eleven women and one man ended up in the hospital after overdosing on a substance police believe may have been slipped into their drinks. All 12 have since been released, a nursing supervisor at a hospital in Ellensburg said Sunday.

Police found no drugs at the home after a four-hour search, and investigators are still looking into what substance may have sickened the 12 and who may have been responsible.

"Some type of drug was slipped into drinks," Ferguson said. "We were talking to people who were highly intoxicated, yet admitted to having only consumed a couple of beverages."

Central Washington University officials issued a statement Sunday, saying the students were safe. Officials said they would review the conduct of individual students, and those in violation of conduct code may face sanctions, ranging from mandated intensive drug and alcohol education course to suspension or expulsion in the most serious cases.

"Although we are deeply concerned about the actions of students who were at the Roslyn house, the fact is that they represent a fraction of CWU students," the statement said.

Roslyn, a former mining town with a population of about 1,000, is where the television sitcom "Northern Exposure" was filmed. The party on Friday coincided with Roslyn Crawl, an event featuring 20 bands at three venues. The party was held at the family summer home of a Central Washington freshman, who police say was extremely cooperative. "He came up with the idea for party and then it took on a life of its own," Moore said.

Students who attended the party described a scene with people falling over and young women vomiting. Some told KOMO-TV of Seattle on Saturday that they believe a bottle of vodka had been spiked with the date-rape drug Rohypnol, commonly known as "roofies."

"Everything was going fine, the music was playing, people were having fun — and then all of a sudden all the girls were puking everywhere," freshman Katelynn Allen told the station. "Girls were outside on their backs."

Student Lindsay Garske told KCPQ-TV of Seattle that "girls were basically unconscious everywhere, all over the house and outside, and it was a very bad scene."

When officers arrived, many partygoers fled. Some crawled into the bathtub and covered themselves with plywood, others crawled into the attic and hid in insulation, Moore said.

"It was chaos," he said.

Officers from Central Washington police helped transport 27 of them back to their residence halls in Ellensburg, about 30 miles away, early Saturday morning, said campus police chief Steve Rittereiser.

Ferguson said his department is planning to meet Monday with other police agencies to coordinate interviews with everyone in the house. They're also waiting for toxicology tests from the state crime lab on blood and urine samples taken from the victims.