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, 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.

But the strategy used in the Myers case “was certainly the most extreme version of the operation that we’ve seen,” said her attorney, Ann Mauer.

According to court papers and to Myers’ account, she and her daughter Kenya, then a 15-year-old high school student, were sitting on the stoop of their building when the sting unfolded

“It seemed like everybody in the Bronx was out that night,” she said in an interview monitored by Vik Pawar, her attorney in her federal lawsuit.

The summer scene was interrupted by a bit of theater staged by police: A dark car raced down the block before stopping. Another vehicle carrying plainclothes officers wasn’t far behind. When the driver got out and ran, the officers gave chase, yelling, “Stop! Police!” her suit says.

Myers’ daughter, seeing that the driver left the car door open, went over and peered inside to see personal items that included what looked like a bundle of cash — in reality, a dollar bill wrapped around pieces of newspaper. The girl had called her mother over when another set of police officers suddenly pulled up in a van and forced them to the ground, according to Myers’ account.

“Get on the floor? For what?” Myers recalled telling the officers.

The officers took them into custody, even though they never touched anything inside the car, the suit says. While entering a stationhouse in handcuffs, Myers spotted the driver of the car standing outside, smoking a cigarette. It dawned on her that he was an undercover with a starring role in the sting — a suspicion supported by the court ruling.

“I thought I was in ‘The Twilight Zone,'” she said.

The girl ultimately wasn’t charged. But her mother spent more than two years fighting charges of petty larceny and possession of stolen property.

A spokesman for the Bronx District Attorney’s office conceded that the bait car had been left unlocked and said prosecutors would not appeal the judge’s ruling. He declined to comment further.

Though defense attorneys in the Bronx say there have been a few other cases involving bait cars and pretend police pursuits, the tactic hasn’t drawn much attention outside the borough.

Donna Lieberman, executive director of the New York Civil Liberties Union and a lucky bag critic, said she wasn’t aware that police were using decoy cars until asked about the Myers case.

“It’s such a bizarre and extreme attempt to set somebody up,” Lieberman said. “It’s like lucky bag on steroids.”

(AP)