A Fairfax County internal affairs police investigation has exonerated an officer in the July 24 shooting death of 19-year-old Robert Staudaher.

Staudaher of 7401 Range Road, in Mount Vernon had held police at bay more than six hours after he barricaded himself in his home and refused to talk with police negotiators, according to a four-page police report released yesterday.

The exonerated officer, Sgt. Daniel P. Grimes, fired the shot that killed Staudaher when negotiations broke down shortly after 4 a.m. Tear gas had been used in a futile effort to subdue Staudaher, who then fired two shots at police officers who had entered the home, the report said.

The report, which was reviewed by county prosecutor Robert F. Horan Jr., also cited incidents earlier on the night of the 23rd and during previous months.

"Robert Staudaher had assaulted both his mother and had punched his father in the mouth, loosening several teeth" the report said. "On previous occasions he has assaulted both parents and police had been called to the home on several occasions during the preceding year . . . because of problems created by Robert Staudaher."

The report also noted Staudaher was being treated by a clinical psychologist at the Mount Vernon Mental Health Center. The report said further psychological assistance was not sought before the shooting because Staudaher's psychologist had said that "if Robert wouldn't talk to the police he would not talk to anyone."

Attempts to reach the Staudaher family for a comment on the report were unsuccessful.

At one point during the incident, when Staudaher's parents and his brother and sister had been evacuated from the home by police, the report said, the mother informed them Robert had been sitting near a room where military weapons were kept.

The report stated that the mother said Robert could remove closet door hinges where the weapons were kept, which the mother said, Robert had done before.

When officers entered the home shortly afterward, the report said, Robert had barricaded himself in his beedroom. Grimes then heard the closing of a weapon bolt, the report said. After tear gas had been tired into the bedroom Robert emerged, firing his gun, the report said. Grimes fired one shot.