An off-duty Jacksonville, FL, sheriff's detective was taking his son to school when he was shot and critically wounded during an impromptu traffic stop, police said Wednesday.

It wasn't immediately clear why the plainclothes narcotics detective chose to stop a white Cadillac, Jacksonville Sheriff's Office Chief Tom Hackney told the Associated Press . The man who shot the officer had just threatened his girlfriend with a gun and was reported as being suicidal.

The detective, who is not being identified because he works undercover, was wearing a "body armor" style vest when he got out of his car to approach the suspect, Hackney said. The word "police" was marked clearly on the vest.

The driver immediately opened fire, Hackney said, hitting the detective in the head, upper body, and hand. The detective was out of surgery Wednesday afternoon and in critical but "more stable condition."

Suspect Kevin Rojas, 19, has been arrested for attempted murder and aggravated battery.

The suspect was shot by police at another location after he reportedly stole a vehicle when he fled the scene of shooting the officer. The suspect is currently in the hospital.