Investigators who set up a sting operation Monday had hoped to snare two corrupt Philadelphia police officers suspected of robbing drug dealers - just not the two who fell into the trap.

The 25th District officers arrested Monday, Sean Alivera and his partner, Christopher Luciano, were not the initial targets of the investigation and were not previously suspected of wrongdoing, sources familiar with the case said.

A confidential informant had identified two other officers as associates of a local drug dealer and had helped set up a sting to catch them robbing a courier of cash and marijuana. The courier was actually an undercover officer.

Investigators said they were shocked when Alivera and Luciano arrived to carry out the scheme instead. Authorities now believe the two targeted officers sent Alivera and Luciano in their places, according to one source close to the investigation.

These disclosures raise the possibility that as many as four 25th District officers have been robbing couriers, stealing cash and giving the drugs to another dealer to sell, sources said.

"I don't know how deep this runs," Police Commissioner Charles H. Ramsey said in an interview Thursday. "We've got a lot of work to do."

He stressed that the case - barely two weeks old - remained in its "infancy." But he also said investigators had no evidence to arrest any other officers from the 25th District, including the two thought to be the targets of the sting.

"We might have been wrong about the people we were looking at initially," he cautioned.

Once the sting netted Alivera and Luciano, Ramsey said, investigators had to spring the trap. They could not allow those officers to remain on the street, even if arresting them meant warning other corrupt officers.

"We're talking about law-enforcement officers. We're talking about people who are making arrests every day," Ramsey said. "If you're ripping off drug dealers, you could end up in a shoot-out. You could end up in anything."

Ramsey expressed his indignation at the corruption and pledged, "If there's anybody else, we'll continue to work it. . . . We'll get them."

He also repeated what he said Tuesday when the arrests of Luciano and Alivera were disclosed: "It could get worse before it gets better."

The case began about two weeks ago, Ramsey said, with a tip from a confidential informant to investigators from the state Bureau of Narcotics Investigations.

The informant said he knew a drug dealer who was bragging about having "boys in blue that could assist him," Ramsey said.

The informant had seen two men who claimed to be officers in the drug dealer's company, but he never saw them in uniform or in a police vehicle. Therefore, sources said, the informant couldn't confirm they were officers.

Investigators then showed the informant mugshots of 25th District officers, and he picked out one. It was that unnamed officer and his partner who were expected to arrive at the sting, sources said.

Authorities had an idea how the drug rip-offs occurred, and Monday's sting operation closely followed the pattern they suspected.

Generally, the dealer working with the officers would arrange a drug purchase somewhere in the 25th District, which includes sections of North Philadelphia and Kensington. When the seller arrived, the officers would stop him and take him away from the scene long enough for someone to steal the drugs from his car.

That's what happened Monday, authorities said, when the undercover officer arrived with $3,000 in cash and 20 pounds of marijuana in his trunk. Surveillance cameras captured the action.

After stopping the undercover officer and putting him in their car, Alivera and Luciano used some pretext to drive him away. During that time, someone believed to be an associate of the drug dealer came and took the marijuana. That person escaped with the drugs, and police were still seeking him on Thursday.

After about 15 minutes, Alivera and Luciano returned with the undercover officer still in custody. One of the officers drove him back to the district in the police cruiser. The other officer got into the undercover operative's car and also returned to the district. The $3,000 was found in the two officers' possession, authorities said.

District Attorney Seth Williams, following the sting operation on an open phone line, then made the call:

"That's enough. Arrest them."

The drug dealer suspected of working with the officers has been identified and also is the subject of the ongoing investigation, sources said.

The arrests of Alivera, 31, and Luciano, 23, came about three months after federal authorities charged three other officers with helping a drug dealer steal heroin.

One of the officers in the federal case, Robert Snyder, also worked in the 25th District. Ramsey said no connection had been established among Snyder, Alivera, and Luciano.

Ramsey said that he could not take any action against the officers who were the initial targets of Monday's sting, and that he had not even learned their names.

"If they turn out to be innocent, I don't want to be associating their names" with corruption, he said.

He also said he hoped the actions of a few officers would not taint the whole department or even the 25th District, which patrols one of the city's toughest areas.

"I'm not going to sit here and deny the fact that we have a problem. . . . You can't hide your warts," Ramsey said. "I do know this: The vast majority of the men and women on this department do this job the way they're supposed to."

Alivera and Luciano are being held on $1 million bail each, according to court records.

On the night of their arrests, sources said, Alivera appeared despondent and ashamed, but investigators were irked by his younger partner's seemingly nonchalant attitude.

Before he went to sleep in lock-up that night, sources said, Luciano took off his police uniform shirt, rolled it up, and used it as a pillow.

Contact staff writer Troy Graham at 215-854-2730 or tgraham@phillynews.com.