A 28-year-old woman and 17-year-old youth were arrested on murder charges yesterday in the death of a mentally disabled man whose burning body was discovered in the woods behind the woman's town house in Dale City.

Police said the two suspects beat 32-year-old Joseph Scott Williams inside the town house early yesterday morning, stole his wallet, dragged him outside and set him on fire. A motorist traveling on a nearby road spotted the blaze and alerted the fire department about 1:30 a.m. yesterday, authorities said.

Yesterday afternoon, police arrested Danita Yvonne Corbin and the 17-year-old youth at Corbin's town house in the 4600 block of Woodway Place, said Prince William County police spokesman Kim Chinn. Corbin and the teenager were charged with murder, robbery and abduction and were being held without bond in Manassas. The 17-year-old, whose name was not released, was charged as a juvenile.

The incident comes two days after a Prince William woman was beaten in front of her two small children. Police say the woman, who died yesterday of her injuries, got into a fight with two teenage girls after she complained that their car was blocking the street.

The two recent crimes are deeply troubling to all Prince William residents, said David Mabie, Prince William's clerk of the Circuit Court and a 30-year resident of the county.

"It's unbelievable. You think it must be a mistake," Mabie said. "We are getting a reputation as a high-tech county and a good, moral place. Just when everything is looking up, then something like this happens. We all perceive it's some sort of setback."

Corbin and Williams were acquaintances, Chinn said. Citing the ongoing investigation, Chinn declined to say how much money was stolen from Williams or whether police believe that robbery was the main motive for the crime. She said it is not clear whether Williams died from the burning or from injuries he suffered earlier.

Corbin's neighbors said Williams often visited Corbin's town house, which is about three miles from the house in Dale City where Williams lived with his parents. His parents, reached at their home, declined to comment.

Williams's friends and neighbors described him as a gentle, caring person who always made a point of greeting them and who was an active member of Evangel Baptist Church in Dale City. They said he was mildly disabled as a result of injuries suffered in a car accident when he was a teenager.

"He cared about people, he was interested in people's salvation, where they were destined to go when they died," said Peggy Kennedy, who lives next door to the Williams family.

The Rev. Jack Keep, pastor of Evangel Baptist, said Williams recently had asked members of the church to pray for a woman named Danita. "He had been very concerned about this woman's situation and requested prayer for her to the church members," Keep said.

Keep said he believed Williams had met the woman while he attended Northern Virginia Community College. "He was concerned about the fact that she was in need--without a job. He was trying to help her," Keep said.

"It's very sad it had to be this way, very shocking," Keep said. "Joe's ministry here on Earth is finished, and the Lord took him home."

Chung Park, 69, an employee at the K-7 Food Mart on Minnieville Road in Dale City, said Williams would come by the store every day to buy coffee. On Wednesday, Williams spoke of a friend who wanted him to lend her $1,500, but he did not name the woman, Park said.

Williams later spoke with a police officer at the convenience store about the situation, Park said. Chinn said she knew of one recent police report in which Williams complained of being threatened, but she would not comment further.

Kennedy said Williams, the oldest of four children, had worked for an electronics store and at a local recreation center. She said that she sometimes saw him mowing lawns in the neighborhood but that he had not been employed recently.

Williams was friendly with several police officers, police said. "Sometimes he'd go to the mall and act like he was a security guard," said Prince William police officer Sean Fuller. "But he was a nice guy. He wouldn't hurt anything."

Police said Corbin was a construction worker. Neighbors interviewed yesterday said they knew little about her. Johanna Gomez, 29, a next-door neighbor of Corbin's, said that she had barely spoken to Corbin and that the house beside her has changed hands three times in three years.

Mabie said the two incidents of brutality in Prince William this week show that no community is immune from terror and violence.

"I don't think it's a sign that our community is coming apart at the seams," he said. "But it's a reminder that we need to redouble our efforts to become a good place to live and where people get along with each other."

Staff writers Christina A. Samuels and Michael D. Shear contributed to this report.