To catch a thief, use a thief. That axiom is especially true in busting drug dealers. Use a drug user to bring down a dealer. Cast a minnow to hook the big fish.

Those minnows are confidential informants — CI’s in police talk.

Whatever they’re called, they can be a cop’s eyes and ears and calling cards. They can vouch for undercover investigators and get them inside the inner circles of criminal enterprises.

Problem is, most CI’s are bad guys, too, with criminal records. That’s exactly what makes them one of the best tools to infiltrate the illegal drug trade. Birds of a feather do drugs together.

“The CI’s have the inside track,” says Stewart Field, a retired New York State Police undercover drug investigator. “They know and have dealt with the bad guys. The bad guys trust them. They have the information, contacts and knowledge that police don’t have.”

That’s why informants were used in the August 2007 Operation Crack Hammer investigation in Elmira that resulted in the arrest of more than 20 drug dealers, says Elmira Police Chief Scott Drake.

“Drugs drive the criminal justice system,” says Richard W. Rich Jr., the Chemung County Public Advocate who has represented hundreds of drug defendants. “Other crimes, like burglaries, robberies and petit larcenies, are done to get money to buy drugs or for the drug dealers to exist.”

Drug investigations are unique and more difficult than say, a burglary. With a burglary, the crime has been committed, and police have evidence, like fingerprints.

But when it comes to drugs, police may suspect someone of selling them, but there’s no crime or evidence until police or an informant actually buys drugs from the dealer. With a drug investigation, the police have to set up the crime and need an informant to make the buy, says Rich.

Where do these informants come from? Some are law-abiding citizens who want to help rid their community of drugs.

But those folks are rare, says Drake. Usually the informants have been arrested, are behind bars or are about to get a long prison sentence, Drake adds. They’re backed into a corner and want to make a deal, like a shorter sentence for helping police catch a bigger fish.

“Or they know we’re breathing down their necks, and they’re going to get arrested next, so they come to us to make a deal,” says Dan O’Brien, a retired Chemung County Sheriff’s Office drug investigator.

The informants know the cops want the ringleaders, and CI’s are willing to cooperate if it will save their hides.

In return, the district attorney may agree to drop some charges against the informants or recommend a shorter prison sentence if the informants help solve a bigger crime.

On rare occasions, the informants receive cash for their information, usually with money confiscated in previous drug busts.

“There were very few that we gave money to,” O’Brien says. “When we did, it could be as little as $20 to as much as $1,000, depending on how badly we needed the information.”

But money isn’t as big of a carrot-and-stick incentive as a promise of reduced prison time. When informants work for cash, their hearts aren’t in it as much as if they were working to get out of jail, say police. And there’s always the possibility that informants may use the money to buy drugs.

Often, police develop and nurture potential informants.

“Let’s say you pull a guy over for speeding, and you know he’s running around with some bad guys you’re investigating,” says O’Brien, owner of O’Brien Private Investigations in Horseheads. “You give him a break. You give him a scolding and let him go, but you do it with the understanding that he will come through with some confidential information for you in the future on a felony.”

Some people may disagree with cutting a criminal a break. If someone does the crime, he does the time. But police say the end justifies the means.

Reliable informants save time and money, and more importantly, they are often the best way to get an airtight conviction against drug dealers, say cops and lawyers.

Police know that using informants is a delicate give-and-take situation that can go bad faster than a speeding bullet.

Informants can lie to investigators and commit crimes while working for police. Once that happens, the deal is off.

“We tell the (district attorney) that the CI was jerking us around, and the DA works to get the maximum sentence possible,” O’Brien says.

That happened years ago with a CI in Corning who was giving investigators information on other drug dealers.

“While he was working as a CI, he was out doing burglaries and drug deals,” O’Brien says. “He was informing on his (drug-dealing) competition to put them out of business.”

That’s why police often put their informants under surveillance or have other informants watch and report back on a new snitch.

“You have to meet with them face to face as often as possible and keep tabs on them,” O’Brien says.

That’s why the cops don’t tell informants much of anything. If they do, it’s to test the informant.

“Sometimes we ask them to get us information we already know to see if what they come back with and tell us is true,” says Field, who worked more than 150 drug cases involving CI’s. “It takes a lot of police investigation work to make sure an informant is reliable.”

Of course those meetings don’t take place at police headquarters or with uniformed officers.

Instead, they meet in a secluded place, like the middle of a rural dirt road or a church or wherever people won’t expect it.

Wherever the contact occurs, though, police always have to be wary of what the CI’s say.

“Never trust them. Every time they tell you something, you have to say to yourself, ‘They are lying,’” O’Brien says. “You have to verify everything they tell you. You have to know what they are doing, where they are going and who they are hanging out with, and make sure they’re not taking information from you and taking it back to the bad guys.

“Nothing is sacred when dealing with informants.”

Jim Pfiffer’s Real Life column about people, places and life in the Twin Tiers appears Mondays, Wednesdays and Fridays. You can reach him by e-mail: jpfiffer@stargazette.com or call (607) 271-8277.