NEW YORK - Sometimes the bait is a small amount of cash in a stray wallet. Or a credit card. Even a pack of cigarettes can do the trick.
Police in New York City leave the items unattended - on subway platforms, on park benches, in cars - and wait to see if someone grabs them.
The New York Police Department says the practice has been a valuable tool for catching career criminals and deterring thefts in public places. But a recent court ruling throwing out a larceny case against a Bronx woman cast a harsh light on a tactic critics say too often sweeps up innocent people.
Judge Linda Poust Lopez found that there was no proof Deirdre Myers tried to steal anything - and that she was framed by a sting that took the tactic way too far.
Upholding the charges "would greatly damage the confidence and trust of the public in the fairness and effectiveness of the criminal justice system, and rightly so," the judge wrote.
Myers, a 40-year-old single mother with no criminal record, has since sued the city, claiming she and her daughter were traumatized by a wrongful arrest in 2010.
"You know how embarrassing and humiliating this was?" Myers said. "I'd never been stopped by the police for anything in my life."
The city Law Department is still reviewing Myers' lawsuit, city attorney Raju Sundaran said in a statement. But, he added, "undercover sting operations are lawful and help reduce crime."
The judge suggested that Myers' brush with the law had its roots in the so-called lucky bag operation that the NYPD began in 2006 to deter thefts of wallets, shopping bags, smartphones and other valuables in the subways.
A typical scenario was for a plainclothes officer to place a handbag with cash on a train platform and briefly look or step away. Anyone who took the bag and then passed up chances to return it to the undercover cop or to report it to a uniformed officer posted nearby could be locked up.
At the time, police credited the subway operation with driving down crime there. They say they still use the tactic when they see a spike in thefts of personal property in public places such as Grand Central Terminal or Central Park. But they now require more evidence of intent - a suspect trying to hide a wallet or taking cash out of it and throwing it away - before making an arrest.
Last year, police arrested a tourist from Atlanta in Central Park after he picked up a purse and took out $27 stashed inside, according to court papers in another pending civil case. He ended up paying a $120 fine as part of a plea bargain.
Authorities began using "bait cars" about six years ago in the Bronx to combat a chronic problem with car thefts and break-ins in working-class neighborhoods. In most cases, police plant property - an iPad, a pack of cigarettes - in plain sight as the bait for thieves but make sure the car is locked so that a suspect would have to take the extra step of breaking in before being arrested.