SCARBOROUGH — A man was in critical condition at Maine Medical Center after being shot outside his vehicle in the parking lot at Walmart on Friday night, police said.

Police did not provide details about the shooting as they collected evidence at the scene and interviewed the people involved.

“The shooter, as well as the female passenger that he was with, have been cooperative with the investigation thus far,” said Maine State Police Lt. Mark Holmquist as he answered questions from reporters after 10 p.m. “They’re being interviewed right now by state police detectives.”

Police investigate the scene of the shooting Friday in the parking lot outside Walmart in Scarborough. Ben McCanna/Staff Photographer

Holmquist said investigators believe the three people involved in the incident knew each other. Police did not share any information about what caused the violence, how the people knew each other, or the type or number of weapons involved.

A witness told News Center Maine that two people were loading groceries into a truck just before 5:30 p.m. when another person walked up and shot at them.

A Scarborough officer who was in the store at the time, investigating an unrelated complaint, responded within minutes and was aided by police officers from South Portland, Holmquist said.

Evidence markers show the locations of shell casings behind the tire of a Toyota Tundra pickup truck at the scene of Friday’s shooting. Ben McCanna/Staff Photographer

Police locked down the Walmart on Gallery Boulevard for nearly an hour. But even after the lockdown was lifted, and customers were allowed to come and go as usual, a section of the parking lot remained cordoned off by yellow police tape.

“Any time we have an incident like this in a public place, the public is in immediate danger,” Scarborough Lt. Tim Barker said. “It did happen very quickly, and it did come to a very quick conclusion.”

“Luckily, no innocent bystanders got hurt, he said.

Investigators spent hours at the scene Friday night, taking photographs and searching the area with flashlights.

A police photographer documents the scene of the shooting, including shell casings near evidence markers. Ben McCanna/Staff Photographer

Multiple vehicles remained inside the police tape. A white pickup truck sat running with its lights on, doors open and a full grocery cart nearby. The icy pavement behind a small dark sedan was marked by what appeared to be blood, and the driver’s door of that vehicle also was open.

Police said later that the pickup belonged to the shooter, and the sedan belonged to the person who was wounded.

Rick Kusturin of Gorham was getting a haircut inside Walmart when the staff announced the lockdown. He said the normally busy store became quiet, and customers waited and whispered by the doors.

“I never felt in danger,” he said.

Police later told Kusturin that he could not go to his car, which was parked close to where the shooting occurred. Police allowed some people to retrieve their cars from inside the taped-off area.

Kusturin and his 13-year-old daughter, Bridget, waited in the lobby for a family member to pick them up. “I came to my dad because I got scared,” the teenager said as they stood with their shopping cart.

Walmart managers said they could not share any information about what happened and directed questions to a corporate media contact.