A Sunday drive, two off-duty cops and a self-inflicted gunshot wound. What went wrong?

Authorities are investigating how an off-duty Alhambra police officer ended up with a self-inflicted gunshot wound after an encounter on the road with an off-duty Los Angeles County sheriff’s deputy.

The San Marino Police Department initially said the driver of a blue Subaru had shot himself after a road rage incident about 8:40 a.m. Sunday near Duarte Road and San Gabriel Boulevard. But on Monday morning, the Police Department said that wasn’t the case.

“At this point in the preliminary investigation, this does not appear to be a road rage incident and neither party knew each other or was aware they were members of a law enforcement agency,” police said in an updated news release.

According to San Marino police, a second driver, identified as an off-duty sheriff’s deputy, told investigators he thought the man in the Subaru was driving erratically.

He wanted to stop the man and ask him not to speed in the neighborhood, he said.

Police said the deputy, who was in a Mercedes-Benz, pulled alongside the other man while they were driving and tried to speak to the Subaru driver, motioning for the man to lower his window.

The Alhambra officer slowed and moved to the right to allow the Mercedes to pass.

The officer later told investigators that the deputy was speeding and that he believed the man in the Mercedes was driving in an aggressive manner.

“Fearing for his safety, the Alhambra officer drew his firearm while inside his vehicle,” San Marino police said.

San Marino Police Chief John Incontro said the officer accidentally shot himself in the process of pulling out his weapon.

Alhambra police said the officer was hospitalized.

“He’s OK,” Alhambra Police Sgt. Rodney Castillo said Monday morning.