SAN DIEGO — Police investigating a burglary at a San Diego veterinary clinic found a badly wounded 88-year-old man and a “concerned citizen” keeping a suspect from leaving the scene, authorities said.

It all started with a call about a break-in around 3:30 p.m. Wednesday at a vet clinic on El Cajon Boulevard near 70th Street, east of the College Area, police said in a news release. Officers showed up and found a person holding a man behind the clinic, waiting for law enforcement.

Officers took that man into custody and then checked the clinic for any victims or evidence of a burglary, officials said. They found an 88-year-old man inside suffering from a serious head wound. He was rushed to the hospital but pronounced dead there a short time later.

While the exact circumstances remained under investigation Thursday, detectives believe the 88-year-old interrupted a burglary inside the clinic, leading to a fight with the intruder. Officials did not say whether they had determined the murder weapon, saying only that during the fight “the victim sustained injuries, including the head wound.”

Police identified the man they arrested at the scene as 37-year-old San Diego resident Patrick O’Brien. He was booked into jail and faces a murder charge, authorities said. They made no mention of burglary counts.

The victim has been identified but authorities said they were not releasing his name until they could notify his family.

Police urged anyone with information regarding the killing to call the San Diego Police Homicide Unit at 619-531-2293 or San Diego County Crime Stoppers at 888-580-8477.