A 16-year-old Fairfax County youth has been arrested and charged with sexual assault, abduction and robbery in connection with two rapes this summer in the Hybla Valley area, and police say he is a suspect in a third attack.

Fairfax County police said the teenager is suspected of entering three homes through unlocked windows or doors and raping female residents at knife point. The youth, whose identity was withheld because of his age, is being held at the Fairfax Juvenile Detention Center.

In two of the cases, police said, the assailant stole cellular telephones from his victims. Investigators were able to use records of calls made from the phones to build a case against the suspect, whose home in the 8000 block of Janna Lee Avenue was searched by authorities when he was arrested Saturday evening, authorities said.

Officer Julie Hersey said the case was unusual because of the age of the suspect and the violent nature of the crimes.

"For a person his age, it is certainly an unusual occurrence," Hersey said. "We don't have these kinds of cases as much with juveniles as we do with adults."

The most recent assault happened early Aug. 2. A 33-year-old woman who lives on Pelican Place told police a man climbed through an unlocked window and held her at knife point, robbed her and sexually assaulted her.

A similar attack occurred July 27 at a 53-year-old woman's home on El Soneta Place, police said. The assailant entered through an unlocked door and robbed and raped the woman at knife point.

On June 20, another woman was attacked in a nearby home, in the 7900 block of Woodpecker Way, in an assault that involved a knife, a robbery and an open window, police said.

The 16-year-old has not been charged in connection with that assault, Hersey said. She said prosecutors are considering whether to charge the youth as an adult in all three cases.

The teenager is not a suspect in a fourth rape in the area on June 19, when a 19-year-old Groveton woman was forced at knife point into a building near Richmond Highway and Memorial Street and raped, Hersey said.