A 50-year-old former Fairfax County man wanted on capital murder charges in the slaying last summer of his co-worker at an Alexandria medical office was arrested in Atlanta yesterday by FBI agents.

Roy Junious Greene Jr. was arrested without incident at his workplace and charged with unlawful flight to avoid prosecution, said Special Agent Greg Horner, an FBI spokesman.

The arrest came four months after Greene was indicted by an Alexandria grand jury in the June 29, 1998, slaying and robbery of Mary Jean Wilcox, 44, a billing clerk at the Association of Alexandria Radiologists. Wilcox, who was found slain at her workplace, had been stabbed repeatedly in the head and upper body, police said.

Authorities yesterday declined to discuss a possible motive for the crime or other details of their investigation. The FBI's Joint Fugitive Task Force concentrated its search for Greene in Atlanta based on a new lead developed by Alexandria detectives, said Lt. John Crawford, a police spokesman. Detectives were heading there last night to try to speak with Greene, Crawford said.

Horner said Greene was working in the service industry in Atlanta, but he declined to identify Greene's employer.

"I was stunned," Sue Wilcox, 50, the victim's sister, said of hearing the news of Greene's arrest. She said she wasn't sure how to react at first. "Do I laugh? Do I cry? Then I flat out got excited."

She said she was having lunch yesterday with a friend at the City Tavern in Manassas when her husband tracked her down to tell her the news. The waitress brought a bottle of champagne to their table.

"I guess my biggest thing now is why it happened," Wilcox said. "We're glad they caught him, so hopefully we'll find out."

Wilcox said that Greene knew her sister only through work and that they never socialized. She said her sister, who was single and lived in Annandale, had talked to their mother on the phone the night before the slaying, saying she had a lot of work to do and would go to the office earlier than usual.

Wilcox's body was discovered at 7:55 a.m. the next day at her office at 2853 Duke St.

Greene worked at the medical office in the evenings and was responsible for locking up and setting the alarm, according to a police affidavit filed in September. Officials at the radiology association did not return a reporter's phone call yesterday.

Sue Wilcox said she has spoken to several of the association's employees about Greene since her sister's slaying. "He didn't strike anyone as having any violent nature," Wilcox said. "There was no animosity between them."

Greene and other co-workers of the victim were interviewed by police the day after the slaying, and Greene became so emotional that the interview was cut short, the police affidavit said.

Two days later, Greene returned to police headquarters to continue his interview, and he denied involvement in the slaying and again became emotional, the affidavit said. It said he disappeared soon after police told him he might be asked to take a polygraph test.

Alexandria Commonwealth's Attorney S. Randolph Sengel has declined to say whether he will seek the death penalty. How soon Greene is brought to Alexandria depends on whether he fights extradition to Virginia, Sengel said.

The Wilcox family recently marked the one-year anniversary of the slaying by attending a morning Mass. Even now, it is hard to believe it really happened, Sue Wilcox said.

"It's still one of those things where you think she's going to open the door and come right in," she said.