Five years ago, she was charged with fatally stabbing her father in a case that was later dropped by prosecutors. Now, Sharon D. Williams is charged with killing her 78-year-old aunt by setting fire to the woman's Northeast Washington rowhouse.

Williams, 49, was arrested about 8 p.m. Monday, less than five hours after the fire swept the home of her aunt, Frances Sanders, in the 600 block of Eighth Street NE. A police source said a dog used by the federal Bureau of Alcohol, Tobacco, Firearms and Explosives detected fire accelerants in the home and on Williams's clothing.

Fire investigators traced more than one apparent point of origin for Monday's blaze -- on the first floor and on stairs leading up to the second floor, the police source said. The accelerant used was gasoline, another source said. Sanders was found dead at the top of stairs on the second floor, with evidence of smoke inhalation and burns.

The arrest marked the second time in recent years that Williams has been charged with killing a relative. In 1997, she was charged in her father's slaying, but prosecutors backed off for reasons they declined to reveal yesterday. According to court documents, Williams told police that she killed her father after he sexually abused her.

Williams, who has a history of mental illness, did not have a steady residence and sometimes stayed at Sanders's three-story home, authorities said, adding that the two argued frequently, including Sunday. That night, the police source said, she and Sanders quarreled about subjects that included the death of Williams's father, Milton Reddick.

According to court papers, the 76-year-old Reddick -- Sanders's brother -- was found stabbed several times in his bed at the Asbury Dwellings, a church-run senior citizens home in the 1600 block of Marion Street NW. Williams told detectives in that case that she had stayed in the home on the night Reddick died, Dec. 13, 1997. She said that Reddick had molested and hit her that night and that she then stabbed him, the court papers said.

Prosecutors filed a manslaughter charge against Williams in her father's death but dropped the case in October 1998.

Although police said Williams had told them that she killed her father, prosecutors did not secure a grand jury indictment. Channing D. Phillips, a spokesman for the U.S. attorney's office, said prosecutors decided that they had "insufficient evidence." He said Justice Department policy and grand jury secrecy rules barred him from talking about a matter that never came to an indictment.

In general, Phillips said, prosecutors consider factors such as the strength of evidence, the existence of self-defense claims and the admissibility in court of any statements made by suspects.

In October 2001, Williams had another encounter with the law when she was charged with assaulting a man with a knife. She later pleaded guilty to one count of simple assault and two counts of destruction of property. She was given a 180-day sentence, according to court papers.

Records in that case show that she has suffered from mental illness. From February to April 2002, Williams participated in the Community Connections program, run by a local organization that provides services for people with mental illness, court records said.

"She met with a psychiatrist regularly and also received counseling to help her heal from her history of extreme physical and sexual abuse," defense attorney John Ostermann stated in court papers filed in the case. He wrote that other officials who evaluated Williams "pointed out the direct relationship between Ms. Williams's history of abuse and illness and her criminal conduct."

Williams began serving her jail term in April 2002. Ostermann tried to get her released early, writing last June that she was not being housed in a mental health wing at the jail.

Williams was released in August and was on probation at the time of Monday's fire.

Contacted yesterday, Ostermann declined to comment about the assault case.

Williams was charged with felony murder in her aunt's death. She is due to appear today in D.C. Superior Court.

Mary Barbour, Sanders's daughter, said yesterday that several of her relatives were home when the fire began and that Williams was in the house at the time. But, she said, none of them saw how the fire started.

"I really don't know what went down," Barbour said yesterday. "I only know my mother's gone."

District firefighters at the scene of Monday afternoon's rowhouse fire in the 600 block of Eighth Street NE.