A troubled teenager who died in a shootout with officers in suburban Washington said repeatedly more than a year ago that he planned to attack a police station, friends of the gunman said.

Michael W. Kennedy, 18, was crouched between two vehicles in the parking lot of the Sully District police station in Chantilly when he opened fire Monday on an officer who had just parked his car.

The officer was hit five times, but was able to call for help on his radio. At least four officers returned fire, but before the shooting stopped a detective was dead and a third officer was wounded. Kennedy lay dead on the pavement, dressed in camouflage fatigues.

Maj. Bob Callahan said Tuesday the teen fired at least 70 rounds from a modified AK-47-style assault weapon and a long-barreled, high powered rifle. Five handguns found on Kennedy's body had not been fired.

Kennedy's classmates recalled that he would sometimes talk about attacking police, but no one ever reported the statements to school officials or authorities.

"He started making those jokes about shooting up a police station about a year ago, but we never took him seriously," said Yasmeen Davis, 18, who graduated with Kennedy last year from Westfield High School.

A few months ago, close friends began noticing a change in Kennedy. His style of dress changed, and he started hoarding weapons and ammunition, and talking increasingly of fighting zombies and aliens.

"He thought he was Jesus," said Brendon Baker, 18, who had known Kennedy since sixth grade.

Kennedy's parents admitted him last month to a psychiatric center in Rockville, Maryland, but within hours, he broke a window and escaped.

Claiming he had a gun, Kennedy allegedly carjacked a sport utility vehicle and drove back to Virginia, where he surrendered to Fairfax County police.

He was returned to Maryland and charged with carjacking and theft. His family posted a $30,000 (euro23,630) bond, and he was expected to stand trial May 24.

Kennedy never returned to the treatment center, but friends said he had been calmer in recent weeks.

"He told me he'd been on medication for a while," Baker said.

Authorities were trying to determine what fueled Kennedy's contempt for police. When they learn more, officials will weigh whether to change security measures at police stations, spokeswoman Mary Ann Jennings said.

Police spent much of Tuesday looking for Kennedy's parents, Brian H. Kennedy, 49, and Margaret J. Kennedy, 44, and an 8-year-old sister who were last seen about the time of Monday's attack. They eventually contacted the family.

An attorney for the family issued a statement from MacDowell & Associates late Tuesday saying that the family was "in seclusion" and that "they are trying to comprehend the tragic events of yesterday."

The statement also offered thoughts and prayers to the family of the detective who was killed.

A note written in crayon and decorated with hearts and stars was taped to the front door of the family's deserted home in Centreville. It read, "No matter where you are, but you will always be remembered, best wishes."

Back at the police station, a squad car was draped in black and covered with flowers to honor detective Vicky O. Armel, 40, who was killed in the attack. Armel's husband, who also is a Fairfax County detective, was in seclusion with the couple's two young children.

The officer who was critically wounded remained hospitalized after surgery. A third injured officer suffered minor injuries.