CHEVERLY, Md. - An undercover narcotics officer was mortally wounded by one of his colleagues as he responded to an attack on his police station by a gunman with a death wish, their police chief angrily explained on Monday.

And while Officer Jacai Colson lay dying, the gunman's two brothers coldly recorded Sunday's firefight on their cellphones, Prince George's County Police Chief Hank Stawinski said, tapping a podium and trying to contain his emotions.

The gunman, Michael Ford, dictated a "last will and testament" just minutes before his two brothers drove him to the station, where he began spraying bullets at passing cars and even an ambulance to draw officers outside, police said.

Colson arrived at the station after the firing began. He was wearing civilian clothes without body armour and leaping out of an unmarked car.

"Police officers run to disorder. They run to the sound of shots," the chief said. "It's my sad duty to have to share with you that, circumstantially, we believe the fired round that led to Detective Colson's death was fired by one of his fellow Prince George's County officers reacting to this."

In the confusion, despite their restraint, one of the other officers' bullets hit Colson, the chief said. Four other officers fired their weapons, and it is not yet known who fired the fatal bullet, said the chief, who praised their restraint as well as the "extreme heroism" of Colson, who "drew fire to himself and in doing so was mortally wounded."

Colson was declared dead later in a hospital. Michael Ford, 22, was expected to survive, along with his brothers Malik, 21, and Elijah, 18. All three were arrested and will face dozens of charges between them, the chief said.

Stawinski said federal agents have determined that there was no larger plot behind the ambush.

"This appears to be the act of the Ford brothers, for their own motives. We have reason to suspect that the Ford brothers did not expect (Michael Ford) to survive his encounter with police," the chief said.

The police union leader, John Teletchea, was livid that the suspects would coldly watch and record what he said their own cellphone evidence shows was an unprovoked and premeditated attack.

Colson, he said, "reacted to protect his fellow police officers and his community. And while doing so we had individuals videotaping, as if it's a game, as if it's something we're going to put on YouTube and glorify.'

The chief said there were no outstanding warrants against the gunman, but that information conflicts with a sheriff's report from Greenville, South Carolina, which said Michael Ford was being sought for allegedly assaulting his wife there the day before.

The attack at 4:30 p.m. Sunday disrupted a quiet, rainy afternoon in Landover, a suburb northeast of downtown Washington, D.C.

Prince George's County State's Attorney Angela Alsobrooks called it "cowardice" and a "horrific act of evil," promising an aggressive investigation and prosecution. The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives also are aiding police, spokesmen for the two federal agencies said.

Colson, who would have turned 29 this week, was a four-year department veteran who worked as an undercover narcotics officer. His football coach at Randolph-Macon College, where Colson played for one year, said he was "a great young man who was well liked and well respected."

"He was just a great human being," coach Pedro Arruza said. "He was a very positive, positive person and an upbeat guy, a good person to be around. He had a lot of friends on campus, everybody liked him. He was just a really high-character guy."

Sheriff's Deputy Dominick Chambers, a friend from the police academy, said they celebrated their four-year anniversary as officers on March 12, the day before Colson was killed.

"He always wanted to be a police officer," Chambers said. "Everyone is taking it real bad, real bad. I'm talking to my classmates, checking in on them. We're not doing well."

Associated Press Writers Juliet Linderman in Baltimore, Ben Nuckols in Washington and Jeffrey S. Collins in Columbia, South Carolina, contributed to this story.