Christian, a University of Tennessee student, and Newsom were on a date Jan. 6, 2007, when her sport utility vehicle was carjacked at gunpoint by several people in Knoxville.

The attackers blindfolded and bound the couple and took them to a rundown rental house. Police concluded Newsom was soon taken away, sexually assaulted, shot in the back of the head, set on fire and left beside some railroad tracks.

Christian was beaten and repeatedly raped over the next 24 hours. An autopsy said she died of suffocation after she was choked, wrapped in plastic bags and dumped in a trash can.

The men, the authorities say, had already strangled Dr. Petit’s wife, Jennifer Hawke-Petit, 48, and in short order would also kill the couple’s two daughters, Hayley, 17, and Michaela, 11. The elder suspect, Steven J. Hayes, 44, had poured gasoline on the girls and their mother, according to a lawyer and a law enforcement official involved in the case, in hopes of concealing DNA evidence of sexual assault. He had raped Ms. Hawke-Petit, and his partner, Joshua Komisarjevsky, 26, had sexually assaulted Michaela.

Moments after Dr. Petit escaped, as the house was being surrounded by police officers, the men lighted the gasoline. The girls were tied to their beds but alive when the gas Mr. Hayes had spread around the house was set aflame.