A Prince George's County police officer was killed Sunday in a fierce shootout with an armed man outside a district station in Landover, in what the police chief said was an unprovoked attack.

Police Chief Henry P. Stawinski III said a man walked up to the District III station and started shooting into the building from the outside. Officers rushed out to stop the attack. Officer Jocai Colson, 28, a four-year department veteran was killed in the gun battle, the chief said. The suspect was wounded and taken to a hospital.

Police have no motive for the attack and have not named the shooter. But the shooter and a man police officials described as his brother were both in custody.

“One of your defenders lost his life in defense of this community today. This was an unprovoked attack,” Stawinski said at a somber news conference Sunday night.

The shooting, which occurred at about 4:30 p.m. at a community center next to the Landover station, prompted authorities to urge residents in the Palmer Park and Landover area to shelter in place as police searched for people connected to the incident. The warning was lifted shortly after 7:30 p.m.

Gov. Larry Hogan ordered flags lowered to half staff. He said Maryland State Police are working closely with local law enforcement to provide support as needed.

“The First Lady and I send our sincere prayers to the family and loved ones of Officer Colson, who made the ultimate sacrifice in service to his fellow citizens and community,” Hogan said. “It is my hope that his proud legacy of commitment and passion for law enforcement and serving others will provide some comfort in the difficult days that lie ahead.”

The shooting comes a month after two longtime Harford County sheriff's deputies were shot to death while on duty in Abingdon.

The slain officer's father, James Colson III, was rushing from Philadelphia to the Washington region Sunday night. His son, he said, “was courageous and an excellent role model” for young men.

Colson graduated from Chichester High School in Boothwyn, Pa., where he was born, and went on to play football at Randolph-Macon College, according to a team roster. Pedro Arruza, the football team's coach, recalled Colson for his strength of character.

“He was a great kid,” Arruza said of Colson, who played one season for the team at defensive back and wide receiver. “A really respectful kid and just a high-character young man. He treated everyone with respect. To be honest, he wasn't a great player, but he was a really great person.”

His high school coach, Joe LaRose, said Jacai Colson's grandfather was also a police officer.

The shooting terrified many in the Palmer Park and Landover areas.

One witness Sunday said she grabbed her sleeping 14-month-old son from his playpen when she heard what she thought was probably firecrackers. She looked out a window and saw a man dressed in black firing a handgun at the police station.

“He fired one shot, and then he started pacing back and forth, then fired another shot,” said Lascelles Grant, a nurse. “Who would shoot a police station on Sunday evening? This is insane.”

Then, police began pouring out of the station.

“Just looking outside, I'm like, ‘Oh my God, look at all these police officers running out, putting their lives really in danger,'?” Grant said. As shooting continued, she ran to her bathroom to take cover, thinking, “Lord, please don't let no shot come inside here and hurt my baby and me.”

Colson was an undercover narcotics officer who worked in high-risk situations, Stawinski said. “When things began to turn, he immediately stepped into action,” Stawinski said of Colson's response Sunday.

The details of what prompted the shooting remain unclear. Police cars and barricades continued to block the area around the police headquarters — also connected to a district station — late into the evening.

“He was always there for his fellow brothers and sisters,” said Prince George's Fraternal Order of Police President John Teletchea.

Prince George's County State's Attorney Angela Alsobrooks called the incident “another horrific act of evil. We have another mother tonight without her son,” Alsobrooks said. She promised an aggressive investigation and prosecution of the alleged shooter.

Police cars and barricades continued to block the area around the police headquarters — also connected to the district station — late into the evening.

Four miles away, in Cheverly, police cruisers lined the entrance to Prince George's Hospital Center. Officers shared hugs and shed tears. They huddled in a circle, holding hands and reciting prayers for their fallen comrade.

The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives have begun assisting local police in the investigation, spokesmen for the two federal agencies said.

FBI spokesman Dave Fitz told the Associated Press that the FBI “reached out and offered support” and sent a couple of special agents to assist. He had no further details.

ATF spokesman Dave Cheplak was unable to say how many ATF agents were assisting or what they were doing. He said the agency typically would help follow up on leads, interview witnesses, support evidence collection and trace any recovered firearms.

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The Associated Press and The Baltimore Sun contributed to this article.