Remains believed to be the girl were found about 3 p.m. in a pond in the 21500 block of Ridegtop Circle in Sterling. During the search, an officer spotted a car driving suspiciously in the area of the search and arrested a man, who is now the subject of the investigation, Fairfax police spokeswoman Tawny Wright said.
Police said they collected several articles of evidence but declined to provide further details.
"I can't think of a worse instance to occur than the loss of a 17-year-old on Father's Day, as the father of a 17-year-old myself," Loudoun County Sheriff Michael Chapman said.
A possible hate crime motivation is among the things authorities are investigating, police said. Loudoun and Fairfax police jointly conducted the search, canvassing an area around Dranesville Road and Woodson Drive in Herndon for hours.
WRC-TV reported that a baseball bat was recovered in the area — information could not be independently confirmed.
Shoyeb Hassan, co-chair of the All Dulles Area Muslim Society in Sterling, identified the girl as 17-year-old Nabra. He did not give her last name.
Hassan said that during the last 10 days of Ramadan, the mosque has extra prayers at midnight and 2 a.m., and members frequently go to McDonald's or the 24-hour IHOP to eat before they start their fast at sunrise, as Nabra, and her friends were doing.
Detectives believe the remains are those of the missing 17-year-old girl, but the Office of the Chief Medical Examiner will confirm the identity and manner of death, Wright said.
The brazen killing rattled a Muslim community in the midst of celebrating Ramadan, a month of religious observance where adherents fast from sunrise-to-sunset for 30 days. The period culminates in the feast-like celebration Eid-al-Fitr, which is expected to fall next weekend.