FORESTVILLE, Md. (AP) — Police are searching for the person who shot and killed an off-duty Maryland state trooper Friday soon after the officer escorted an unruly customer from a restaurant over a disputed bill.

Trooper 1st Class Wesley W. Brown, 24, escorted the customer Thursday evening from an Applebee’s, and when Brown left the restaurant around 12:40 a.m. Friday, someone shot him, Prince George’s County Police spokesman Maj. Andy Ellis said.

Ellis said police had not identified a suspect. State Police Superintendent Col. Terrence Sheridan said earlier that the disorderly customer, who fled, was the shooter, but Ellis said investigators had not been able to confirm that. Ellis called that customer a person of interest and said police were trying to determine if other people were involved. Investigators found multiple shell casings, but there was no indication more than one weapon was used.

Brown, who wore a jacket that identified him as an officer, was talking on a phone in the parking lot when he was shot, state police said. He was working a second job as a security guard at the restaurant, as was a retired state police trooper who was also present.

Covered in blood, Brown made it back inside the restaurant and passed out, police said. Ellis said that Brown was wearing a vest, but it did not stop the bullet from entering Brown’s upper body and hitting his heart. He died at a local hospital.

‘‘This is a cold-blooded killing,’’ Ellis said. ‘‘This person is dangerous.’’

Ellis urged the suspect to surrender.

‘‘We’re going to find out who he is. There’s no question,’’ Ellis said. ‘‘There has never been an unsolved police shooting (in the county).’’

Investigators have spoken to more than 50 witnesses who were at the restaurant Thursday night, Ellis said. Detectives will also review surveillance video from the restaurant and surrounding businesses.

Gov. Martin O’Malley announced that flags would be flown at half-staff in Brown’s honor.

Brown’s cousin Kenneth Pollard, 48, visited the scene Friday.

‘‘He was a good guy and he tried to do the right thing and somebody took his life,’’ he said.

He said Brown had eight older sisters and an older brother who works for the FBI in Washington.

‘‘He was a funny guy, happy-go-lucky, always smiling,’’ he said.

Brown was recently engaged to be married, said state police spokesman Greg Shipley.

Many troopers do security work part time, but such jobs must be approved by the state police command, he said. Brown’s part-time job, which he used to supplement an annual salary of about $47,400, had been approved.

Eugene Grant, the mayor of nearby Seat Pleasant, called Brown a ‘‘beacon of light’’ who grew up in the community and was well known. Brown had mentored hundreds of people through the mentoring group he founded in 2007, called Young Men Enlightening Younger Men.

First Sgt. Rodney Morris, the assistant commander of the Forestville state police barrack where Brown was assigned, described him as a remarkable young man and said whenever there was a community event, Brown was one of the first he chose to participate.

‘‘All he wanted to do was serve his community and Prince George’s County,’’ Morris said.

He said Brown planned to take young people Friday on a trip to New York, paying for the trip himself so the youngsters could visit landmarks and historic sites. With Brown’s death, Morris said another mentor led the trip.

A 2007 Maryland Gazette article about the group said Brown ran into problems himself as a teenager, including being kicked out of high school for fighting, but had turned his life around. He wanted to inspire teens to do the same.

William Hodge, who works at the Old Country Buffett next to the Applebee’s, said there have long been safety concerns in the area and that it’s not unusual for restaurants to hire security.

‘‘I wouldn’t walk up this road at 1 o’clock in the morning,’’ Hodge said. He said there have been robberies, vandalism and incidents where customers have attacked employees at nearby restaurants.

Still, ‘‘this is extreme right here, killing a cop, you just don’t do that,’’ he said. ‘‘This is going to put the criminals here on high alert.’’