A soldier who shot his roommate to death in February in Annandale has pleaded guilty to involuntary manslaughter in a closed military proceeding and will serve 41/2 years in military prison, the Army disclosed yesterday.

Wayne S. Grimm, 22, initially was arrested by Fairfax County police and charged with manslaughter in the Feb. 13 shooting of close friend Michael Kenagy, 24. They were members of the Army's ceremonial Old Guard unit at Fort Myer in Arlington.

When the Army sought to prosecute the case, Fairfax Commonwealth's Attorney Robert F. Horan Jr. agreed and turned Grimm over to the Army in April.

The Army promptly released Grimm from custody -- he had been held without bond in Fairfax, as is standard practice for homicide cases -- and officials at the Military District of Washington declined to answer repeated inquiries about the case. Horan said the Army had told him Grimm would remain in custody.

On Tuesday, a court-martial hearing was held for Grimm, Army spokeswoman Barbara Owens said. Although initially charged with murder, Grimm entered a guilty plea to involuntary manslaughter, Owens said.

The hearing was not open to the public.

Grimm will serve his sentence at the Regional Correctional Facility at Fort Knox, Ky., Owens said. Grimm, who held the rank of specialist, was reduced to private, will forfeit all pay and allowances and will receive a "bad conduct" discharge, she said.

No details about the hearing -- such as whether witnesses or family members testified, what the facts were about the killing or who ruled on the case -- were available, Owens said.

Neither the Army's staff judge advocate, Col. Sarah Green, nor her staff, which prosecuted Grimm, would discuss the case, Owens said. Grimm's attorney, Capt. Gabe Hinkebein of the Army's Trial Defense Services, also declined to talk about the case.

A message left for Gen. Galen B. Jackman, commanding general of the Military District of Washington, received no response yesterday. Jackman was responsible for deciding what charges and what type of court-martial Grimm faced, an Army official said in April.

Kenagy's father, Michael Kenagy Sr. of Hubbard, Ore., attended the hearing, a family member said yesterday. He was returning to Oregon yesterday and did not respond to a message left at his home.

Grimm and the younger Kenagy lived in an apartment in the 6800 block of Perry Penney Drive, off Little River Turnpike. Court records stated that the two argued about whether one was playing his music too loudly.

Grimm fired a handgun at his bedroom door, not knowing that Kenagy was standing behind it, police said. The single shot killed Kenagy, authorities said.

Grimm cooperated with Fairfax police and gave a statement to Detective June Boyle, Horan said.

Army investigators later picked up the case and obtained information from Fairfax police. But the Army did not inform Boyle or Horan about Tuesday's hearing or the case's resolution.

Horan said he thought an involuntary manslaughter conviction was appropriate.

"He shot through the bedroom door," Horan said, "and he hit the victim. It was very iffy as to if he knew the victim was behind the door. I think he told Boyle he didn't realize [Kenagy] was behind the door."

Horan said the sentence was "certainly in the ballpark" of a proper sentence. Grimm faced a maximum sentence of 10 years for involuntary manslaughter in state court.

Spec. Wayne S. Grimm, 22, pleaded guilty to manslaughter.