MILTON, Mass. -- Flags were lowered to half-staff at the Milton Police Department on Tuesday after an off-duty police officer was killed in a car crash.

NewsCenter 5's Janet Wu reported that Detective Michael Devin, 57, died when his car was hit head-on by a wrong-way driver on Route 1 in Chelsea Monday night.

"There was an report of an erratic operator on the Tobin Bridge and that this operator, at one point, rear-ended a vehicle just before the toll booths and then backed up the vehicle, put it in reverse, and then started heading the wrong way northbound in the southbound lane," said Milton Police Deputy Chief Paul Nolan.

A passenger with Devin, Ann Condon, a secretary at the police department, survived.

"Detective Devin, obviously, moved the car quickly to the right so the full impact was to the driver's side," said Nolan.

The driver of the car that hit them, Stephen Tarnell, 50, of New Hampshire, was also killed. State police said they do not think alcohol was involved and said an existing medical condition might be to blame.

"The state police said they believed it might have been a diabetic reaction, but we are not sure. We are still waiting for more information," Nolan said.

Devin's brother-in-law Jim Mullen said the family is in shock. He leaves behind a wife and three children.

"(Last week) Mike says, 'Well, I am thinking about the first of the year I'll retire.' That was Thursday. He will never know. You always have to live for today -- tomorrow may never come," Mullen said.

"It is a complete tragedy for him, his wife, his children. You would hope after somebody put 35 years into his career as a police officer, they would be able to enjoy life. But, unfortunately, it is not going to happen," Nolan said.

Condon was released from the hospital on Tuesday. "There was an report or an erratic operator on the Tobin Bridge and that this operator, at one point, rear ended a vehicle just before the toll booths and then backed up the vehicle, put it in reverse, and then started heading the wrong way northbound in the southbound lane," said Milton Police Deputy Chief Paul Nolan.

A passenger with Devin, Ann Condon, a secretary at the police department, survived.

"Detective Devin, obviously, moved the car quickly to the right so the full impact was to the driver's side," said Nolan.

The driver of the car that hit them, Stephen Tarnell, 50, of New Hampshire, was also killed. State police said they do not think alcohol was involved and said an existing medical condition might be to blame.

"The state police said they believed it might have been a diabetic reaction, but we are not sure. We are still waiting for more information," Nolan said.

Devin's brother-in-law Jim Mullen said the family is in shock. He leaves behind a wife and three children.

"(Last week) Mike says, 'Well, I am thinking about the first of the year I'll retire.' That was Thursday. He will never know. You always have to live for today -- tomorrow may never come," Mullen said.

"It is a complete tragedy for him, his wife, his children. You would hope after somebody put 35 years into his career as a police officer, they would be able to enjoy life. But, unfortunately, it is not going to happen," Nolan said.

Condon was released from the hospital on Tuesday.