PORTLAND, Maine — A 27-year-old security guard at Mercy Hospital was fatally shot early Sunday while outdoors on his break, police said.

After hearing gunshots, hospital employees found James Angelo wounded in a fenced-in hospital parking lot. He was treated in Mercy’s emergency room before being transferred to Maine Medical Center, where he died, police said.

Witnesses told police that two people walking along Winter Street “had some kind of engagement with the victim” and fled in opposite directions after shots were fired around 4 a.m., Chief Joseph Loughlin said.

Police said one of the two was described as a short black man in his early 20s with a slight build, short black hair and apparently clean shaven, wearing black pants and a white hooded sweatshirt with a design or print. The other person was described only as wearing a light-colored shirt or jacket.

Angelo and his family had arrived in Portland from the Sudan in 1995.

“It’s a good family,” said Loughlin, recalling how he helped move them into the Parkside neighborhood when he patrolled the area.

Loughlin vowed that the perpetrators will be brought to justice.

Police declined to reveal details of the investigation. Asked if the shooting was a random event, Loughlin said, “We really don’t know yet. Of course, it was raining last night, it was dark, it was still stormy. We’re still trying to discover the facts and circumstances.”

The hospital’s security guards wear uniforms but are unarmed, he said.

Loughlin urged anyone who may know the identity of the two people who fled the scene to contact police.

“I’m sure someone knows what happened out there,” he said. “We need help from the public on this.”

At least six detectives, along with patrol officers, were working on the case Sunday, Loughlin said, and arrangements were being made for an autopsy.

Loughlin said he was unaware of any lockdown at Mercy or changes in operation following the shooting. The hospital had no comment on the shooting, according to an employee who declined to give his name.