The police call them gym creepers, thieves who break into lockers while the unsuspecting victims are working out.

A creeper struck the locker room at Bally’s Total Fitness on Jamaica Avenue in Queens on May 2, making off with a man’s duffel, containing credit cards, boxing equipment, sneakers, a headphones and $22. The thief returned four days later and cleaned out the lockers of three other men, stealing wallets, credit cards, phones and cash, and on the way out, a fourth man’s bicycle.

He struck at another gym the next week, on the ground floor of a building on Kew Gardens Road that also contained offices of the Federal Bureau of Investigation and the Queens County district attorney. But this creeper was identified from what, in precinct geography, was a world away, in a new, sixth-floor office at 1 Police Plaza in Manhattan, by a detective who never laid a hand on the suspect or spent a moment in the same room with him.

The detective, Maria Lopez-Cruz, reading through a daily stack of larceny complaints, noticed several gym incidents, and a picture of the suspect from a surveillance camera in Queens. She searched for similar crimes in the police database, narrowing the list by race and approximate age, believing that gym creepers, like pickpockets, purse-snatchers and other types of thieves, tend to steal the same way, over and over.