The undercover officers started to appear at San Diego State fraternity parties about six months ago.
They dressed like students, complained about their parents and professors, and talked freely and knowingly of things of great interest on campus: music, sex and drugs.
Soon they were accepted, with no questions asked. They were spotted at student hangouts on and off campus. They swapped cellphone numbers with other partygoers. They text-messaged their newfound friends.
The real students appeared to accept the pretend ones -- most but not all of whom were men. On a campus of 34,000 students, blending into the crowd was not difficult. Neither was collecting evidence of drug dealing and drug use.
On Tuesday, authorities announced that 96 young men -- including 75 students -- had been arrested on a variety of drug charges as a result of Operation Sudden Fall, which infiltrated seven fraternities on Fraternity Row and Fraternity Circle. Officials said the name of the operation referred to the prospect of sudden death from drug usage.
The investigation involved marijuana, cocaine, methamphetamine and Ecstasy.
One of the alleged drug dealers is 19 and recently had been praised as a model student in a university publication. Another was just a month away from earning a master's degree in homeland security and had worked with the campus police as a security officer. One allegedly was selling cocaine to high school students.
A criminal justice major was arrested on suspicion of possession of cocaine. As he was being arrested, he asked officers if this would hurt his chances for a law enforcement career, officials said.
Among the suspected drug dealers is Omar Castaneda, 36, who is not a student and is allegedly connected to a gang in Pacoima that has possible ties to the Mexican Mafia, said Ralph W. Partridge, a special-agent-in-charge for the Drug Enforcement Administration in San Diego.
"This operation shows how accessible and pervasive illegal drugs continue to be on our college campuses and how common it is for students to be selling to other students," said San Diego County Dist. Atty. Bonnie Dumanis.
University police began the investigation a year ago after a 19-year-old female student died of cocaine and ethanol intoxication, San Diego State President Stephen Weber said at a news conference Tuesday morning at the district attorney's office.
About six months ago, the probe was broadened to include agents from the federal Drug Enforcement Administration and youthful-looking undercover officers from several local police departments, who quickly became regulars at the weekend party scene.
During the investigation, a 24-year-old student at San Diego Mesa College died of a cocaine overdose after a party at a San Diego State fraternity house. None of the arrests Tuesday was linked to the two students' deaths, officials said.
About 20 of the arrested students were involved in selling drugs, authorities said. The remainder were arrested on suspicion of possession. About 130 drug purchases were made during the investigation, both on and off campus.
Deputy Dist. Atty. Damon Mosler, head of the district attorney's narcotics unit, said the operation was so successful that the alleged drug dealers sold narcotics to people they didn't know on the basis of undercover officers' referrals. More experienced drug dealers would never exhibit such carelessness, Mosler said.
Weber, the university's president, said he did not hesitate to allow undercover officers on campus, even if that decision sparked ire.
"We did the right thing," he said. "I think, frankly, more universities should step up and take these kinds of actions."
As for those responsible for drug dealing, he said, "if we find that the fraternities as organizations were involved, they will be kicked off campus."
Several members of the Theta Chi, Phi Kappa Psi and Delta Sigma Pi fraternities were arrested.
Late Tuesday, the university announced the suspension of six fraternities -- Lambda Chi Alpha, Phi Kappa Psi, Phi Kappa Theta, Theta Chi, Sigma Alpha Epsilon and Sigma Alpha Mu -- pending a hearing into their involvement in the drug dealing.
All of the arrested students have been suspended, Weber said. Those who live in university-owned or maintained housing are being evicted, he added.
On the sprawling campus in eastern San Diego, word of the drug busts spread rapidly.
Angela Beckwith, 22, a child development major, said the arrests "are a shocker but not really a surprise. Lots of people are using."
"I'm surprised more people aren't caught or get hurt," said Adam Klein, 23, a business major and a member of the Phi Kappa Theta fraternity. "This looks bad for the whole Greek system."
One suspect, Kenneth Ciaccio, 19, a member of the Theta Chi fraternity, sent out a mass text message early last month to "faithful customers," saying that he was traveling to Las Vegas and would not be able to make his normal cocaine sales, the DEA said.
A publication produced by the university's public relations department that recently lauded Ciaccio as a model student was taken off its website Tuesday.
Although the investigation was widely praised in San Diego, the nationwide group Drug Policy Alliance blasted it as "sensationalistic" and futile. The group believes in the decriminalization of marijuana and favors increased drug education and treatment over mass arrests.
"College students on any campus in this country are easy pickings," said Margaret Dooley-Sammuli, the group's deputy state director for Southern California. "But these types of arrests are not the best use of the DEA's resources. They should be targeting large-scale traffickers and distributors."
According to the DEA, the seized evidence included 4 pounds of cocaine, 50 pounds of marijuana, 48 hydroponic marijuana plants, 350 Ecstasy pills, 30 vials of hash oil, methamphetamine, psilocybin (mushrooms), various illicit prescription drugs, a shotgun, three semiautomatic pistols, three brass knuckles and $60,000 in cash.
Officials put the value of the seized drugs at more than $100,000. They said the marijuana was high-grade and probably grown locally because marijuana smuggled from Mexico is usually of a lower quality.