The Bourne Supremacy star Matt Damon worked with members of the Massachusetts police force for three days, in order to gain some experience for his new role as an undercover police officer.

Damon decided that training was necessary for his role in The Departed, which also stars Leonardo Dicaprio and Jack Nicholson.

"We showed him frisk tactics and pat downs - and no, we didn't try them on him," state police Sergeant Daniel Risteen is quoted by Teen Hollywood as saying.

"He seemed like he had a pretty good working knowledge [already]. Things weren't going over his head."

On his final night of training, Damon watched as three suspects were arrested, and detectives recovered $1,000 in drug money and paraphernalia.