A Middle Island man allegedly impersonating a cop was arrested Tuesday after a real police officer caught him in the act.

Suffolk Deputy Sheriff Michael Brecht says he was on the LIE early Tuesday morning when he saw what looked like an undercover cop in an unmarked car pull over a minivan for a traffic stop. Police say the accused cop impersonator, 39-year-old Juan Santiago, was wearing body armor and driving an unmarked Crown Vic with flashing lights. Brecht says Santiago signaled to him he needed help with his ?traffic stop,? which raised a red flag.

"He seemed to indicate he wanted me to write her a ticket for speeding,? Brecht says. ?I told him I wasn't able to do that because I didn't witness it and then I realized any cop would know that and I grew suspicious.?

Brecht called for backup and arrested Santiago. Sheriff Vincent DeMarco says the department had reports of the car on the road and had been on the lookout for it recently. He says he doesn't know how long Santiago had been dressing as cop.

DeMarco says his department does not use unmarked cars to make traffic stops, especially at night. He encourages drivers to call 911 if they?re suspicious of anyone who pulls them over.

AP wire reports contributed to this article.