A lot of training goes into turning someone into a New York City police officer.

That’s according to the former head of the police academy at the New York Police Department.

Chief James Shea is testifying at a trial challenging the legality of some of the 5 million street stops made by police in the past decade. He continues Monday.

Shea testified about some of the ways officers recognize suspicious behavior. They’re trained to look for strange bulges in pockets, awkward movements and hand gestures that may give away the fact that someone is hiding a gun.

But officers must have reasonable suspicion.

The testimony was offered to show that police officers are properly trained on how to stop people on the street.