Robin and Donald Peters had been fighting for months -- loud, angry arguments that rattled their Chillum neighbors. During one fight, Robin went into the hallway of their apartment building and pulled the fire alarm, summoning the authorities, a neighbor recalled.

On Thursday evening, it was her brother who intervened, authorities and neighbors said. By the end of the night, Patrick B. Elliott, 35, was dead of gunshot wounds and his sister's husband, Donald J. Peters, 39, was in police custody, facing first-degree murder charges.

Prince George's County homicide detectives yesterday were attempting to piece together the events that preceded the shooting. Law enforcement officials and neighbors gave an account of events:

Robin and Donald Peters were fighting shortly before 11 p.m. when Elliott arrived to visit his sister at the apartment in the 5800 block of Timber Creek Terrace.

Elliott, who lived in the District, asked his brother-in-law to step outside, and Donald Peters obliged. After a few minutes, Peters ran into the apartment. Elliott followed him.

A police report indicated that Elliott had a baseball bat. A neighbor, who declined to be identified because she is a witness, said Elliott was carrying a three-foot stick.

Then a shot was fired.

"It was a boom. Then there was a pause. Then there was a bunch of shots, eight or nine rounds," the neighbor said.

After the shooting, Peters called police and identified himself, then said he had shot his brother-in-law, authorities said. He said police should come and lock him up.

Peters remains in jail on murder charges; his bond hearing is scheduled for Monday.

Prince George's State's Attorney Glenn F. Ivey said the circumstances of the shooting are under investigation. He declined to classify the case as a domestic violence-related crime. But he said the shooting underscores how important it is for people in volatile family situations to seek help.

"When an issue comes up, get help. It's okay to call the police or a family crisis center or a social worker," Ivey said. "You don't have to resolve these things by yourself."

October is Domestic Violence Awareness Month nationwide. On Sunday, Ivey spoke at two churches in the county on the issue and is scheduled to speak at another church tomorrow.

Lydia Watts, executive director of Women Empowered Against Violence Inc., an advocacy group in the District, echoed Ivey's comments.

"At that moment of crisis, the most important thing is to call the police rather than to try to intercede," Watts said.

Efforts to reach Robin Peters, 39, were unsuccessful and no one answered the door at her apartment.

Donald Peters has a lengthy criminal record in Prince George's and Montgomery counties, according to court records.

In 1998, he pleaded guilty to stealing four tires from a merchant in College Park. He was sentenced to one day in jail, according to Prince George's court records.

In 1995, Peters was convicted of robbery and battery in Montgomery. While working as a pizza deliveryman the previous year, Peters punched a man and stole $49 from him, Montgomery records show.

Peters later was convicted after he knocked a wallet from a man's hand, grabbed the money that came out and fled.

Staff writer Rebecca Dana and Metro researcher Bobbye Pratt contributed to this report.