An Acton police supervisor has been placed on leave subject to an internal affairs investigation after allegedly not charging a retired police officer with a suspected OUI and driving him home instead, Acton Police announced late Monday.

At 12:41 a.m. Saturday, an Acton Police officer and a new patrol officer in training were conducting a check of a liquor store parking lot on Main Street and noticed a 2024 Toyota Highlander running in the lot, the department said.

A man sitting in the driver’s seat — identified by the department as a retired police official from another community — immediately exited the car as the officers approached the vehicle, according to Acton Police. The cops then called in a supervisor to respond to the scene.

The officers noticed “odor of alcohol on the vehicle owner’s breath” and an open can of Twisted Tea brand malt beverage visible in a cup holder. The car had a “severely flat” passenger side front tire, and “no other damage was noted,” the department said.

Upon arriving at the scene, the police supervisor took the retired cop back to his home in Acton, Acton Police said. The other officer was “instructed by the supervisor” to drive the passenger, a 55-year-old Acton woman, back to her home.

The next day, Acton Police commanders including Chief James Cogan and Lieutenant Ed Lawton reviewed the incident, the department said.

A decision was made to file charges of Operating Under the Influence and Possession of an Open Container of Alcohol in a Motor Vehicle. The man has been summons to Concord District Court.

The Acton Police Department said they are not yet releasing the man’s name, identifying him as a 64-year-old, as a criminal complaint has not been issued as of Monday night.

An internal affairs investigation has been launched into the supervisor’s handling of the matter, the department said. The supervisor has been placed on administrative leave pending the outcome of the investigation, “consistent with the policies of the Acton Police Department and the Department’s collective bargaining agreement.”

The Middlesex DA and Acton Town Manager have also been contacted and notified.

“The Acton Police Department is a modern, state-accredited police department, and the laws we swear to apply to our residents apply equally to current and former members of law enforcement agencies,” Cogan said. “Our public rightly demands that we enforce the law evenly, and we will conduct a full and thorough review of the handling of the situation that unfolded early Saturday morning.”