A Philadelphia police inspector was arrested Thursday, along with his brother, and accused of beating a man after falsely accusing him of breaking into cars in their Northeast neighborhood in August, authorities said.

Inspector James Smith, 52, and his brother, Patrick Smith, 53, a former city police detective who retired shortly after the incident, were charged with simple assault, conspiracy, and recklessly endangering another person.

Police Commissioner Danielle Outlaw said Smith will be suspended for 30 days then fired.

“The charges against Inspector James Smith are disturbing, and allege behavior that is in stark contrast to everything that society expects of its police officers,” she said.

John McNesby, president of FOP Lodge 5, the union that represents city police officers, criticized District Attorney Larry Krasner for charging the two men.

“Once again, DA Krasner is only interested in arresting Philadelphia police officers to save his failing reelection campaign,” he said. “We support our officers and they deserve a vigorous defense against these baseless charges.”

Shortly after midnight Aug. 19, the Smiths, who were off duty and in a car, chased the victim, who was on foot, from their neighborhood to the parking lot of a shopping center near Fairdale and Knights Roads. After getting out of the car, the brothers caught up to the victim and slammed him repeatedly against a wall and threw him to the ground causing injuries including a black eye and abrasions on the back of his head, elbows, and knees, authorities said. The victim, 27, is autistic, they said.

The two men falsely told the victim they were members of a neighborhood town watch, and repeated that lie when the victim’s father — who tracked his son by a phone app — showed up at the scene, Krasner said.

“The allegations here involve vigilantism and brutality against civilians, which cannot be tolerated,” Krasner said. “It is truly disturbing that the victim, who has Asperger syndrome, may have struggled to communicate his distress and fear.”

Outlaw said: “It is imperative that police officers repair community trust in order to effectively do their jobs. In order to do this, we must prove that we are committed to identifying and removing bad actors from within our ranks.”

Smith, a 30-year department veteran, was last assigned to the Forensic Science Bureau and was paid $134,629 annually.

After retiring on Sept. 3, Patrick Smith went to work for the Philadelphia Gun and Violence Task Force, which is funded by the state and is part of the state Attorney General’s Office. He has been placed on administrative duty, where he will remain until the resolution of his criminal case, a spokesperson for the office said.