Joseph C. Vignola Jr. and a Philadelphia high school senior met on Craigslist, the Web site popular for its personal ads, police said.
Vignola, 19, the son of a former city councilman, and the 18-year-old woman saw each other at least once before they got together Wednesday at the North American Motor Inn on City Avenue, police said, and that night, they had consensual sex in one of the hotel rooms.
Then Vignola and the woman had an argument, and he slashed her throat with a knife, police said.
Vignola was arrested Friday night and charged Saturday with attempted murder and related offenses, including unlawful restraint and false imprisonment. Vignola, of the 6400 block of Drexel Road in the city's Overbrook Farms section, was not charged with a sex crime.
He has been released after his parents posted 10 percent of his $250,000 bail. His father is Joseph C. Vignola, a former city controller and councilman.
The senior Vignola, who lives in South Philadelphia and this year pondered entering the state Senate race in his district, did not return a phone call seeking comment.
The victim is recovering at Thomas Jefferson University Hospital after neck surgery, said Capt. John Darby, commanding officer of the Special Victims Unit.
Darby said the woman, despite her wound, was able to call 911 and told the operator that she was losing consciousness from bleeding.
"This girl almost lost her life," Darby said.
Initial police reports were that the woman was bound with a shirt, but Darby said further investigation found no evidence of that.
He said the false imprisonment and unlawful restraint charges stem from Vignola's not letting the woman leave the room.
Vignola surrendered a knife to police, and it is being examined for forensic evidence, Darby said.
Darby said Vignola and his family were being very cooperative.
Investigators were led to Vignola based on information developed from an anonymous tip phoned into police the day after the alleged assault, Darby said.
Vignola attended Valley Forge Military Academy and College from fall 2006 to fall 2007, an academy spokeswoman said. He left after the start of his senior year and did not return.
His father last held elected office in 1995, when as a first-term councilman he resigned to become executive director of the Pennsylvania Intergovernmental Cooperation Authority. He remained in that job for 10 years. Before that, he was city controller from 1983 to 1987.