But Nabra's family feels certain she was abducted and killed because she was wearing Islamic clothing as she returned to the All Dulles Area Muslim Society mosque in Sterling after the group had gone out for a late night bite to eat amid their Ramadan observance.
Nearly 12,000 people had signed a petition calling for state and federal probes of Nabra's killing as a hate crime.
A Muslim civil rights and advocacy organization criticized police on Tuesday for settling too soon on road rage as motivator and said the killing should be seen in the context of a rise in hate crimes targeting Muslims across the country.
"We think it's premature," said Ibrahim Hooper, a spokesman for the Council on American-Islamic relations known as CAIR. "We believe these incidents are at the core motivated by the perception that these subjects are Muslim."
Nabra's family has said she was wearing a long women's garment known as an abaya and a hijab head covering.
Her funeral is set for 1:30 p.m. Wednesday at the Sterling mosque, Hooper said.
Her beating, abduction and murder were clearly hateful acts, but bringing formal hate crime charges is more complicated. Proving a hate crime in court requires showing overt bias, that a person was motivated, for instance, by the victim's religion, ethnicity, national origin or gender.
According to the police, Darwin Martinez Torres, a 22-year-old construction worker, argued a teen on a bike who was part of the group before jumping a curb with his car and chasing the larger group before catching up to Nabra in a parking lot, where he is accused of hitting her with a baseball bat, abducting her and later killing her. The other teens reported what had happened — and that Nabra had fallen as they all fled — when they got back to the mosque around 4 a.m. Sunday, prompting a police search by Fairfax and neighboring Loudoun counties and the arrest of Torres within hours after a Fairfax officer noticed Torres circling near the crime scene, police have said.
Nabra's body was found in a pond Sunday afternoon based on leads that police have not detailed.
Fairfax County police said at a Monday news conference they have turned up no slurs or other evidence that Martinez Torres was motivated to kill Nabra because of her religion.
Even so, they continue to probe the case and would revise their initial assessment if evidence of a hate crime is found, they have said.
Most hate-crime cases are handled by state prosecutors and typically carry stiffer penalties than crimes charged without a bias component. Forty-five states and the District have specific hate-crimes laws. But most differ on what acts qualify and some leave it to judges to decide whether to impose stiffer penalties at the time of sentencing.
Virginia's hate-crime statute includes penalty enhancements for crimes motivated by race, religion and ethnicity. The Commonwealth's law is not as comprehensive as measures in Maryland or D.C. that also cover bias related to gender, sexual orientation, disability and gender identity, according to the Anti-Defamation League (ADL).
Federal hate-crime charges generally carry even harsher penalties than state statutes. Federal prosecutors in Northern Virginia have not opened an investigation at this point.
Beyond the tougher potential punishment, formally attaching the hate-crime label in court can signal to the broader community that certain heinous acts are different because of their intended impact.
"Such incidents send shock waves through the entire community and have the potential to make communities feel unsafe and vulnerable," ADL's Washington regional director, Doron F. Ezickson, said in a statement. "We must come together to send an opposing message that all people, regardless of their religious or ethnic background, are safe, welcome and protected."
Ezickson said Tuesday his organization is monitoring the investigation and has "every confidence in law enforcement to determine what happened to Nabra and whether the circumstances of her death merit a hate crimes charge."
Hooper, the CAIR spokesman, compared Nabra's killing to a North Carolina case in which three Muslim college students were shot and killed in 2015. Police determined Craig Stephen Hicks's motivation for killing the students in Chapel Hill was a parking dispute, but many Muslim groups thought it was a hate crime.
The FBI and the Department of Justice opened a probe to determine if the case was a hate crime. No federal charges have been filed.
Nabra's father told detectives that he believes his daughter was killed because of her religion. "Why was he running behind the kids wearing Islamic clothes with a baseball stick? Why, when my daughter fell down, why did he hit her? For what?" Mohmoud Hassanen said.
"We don't know this guy. He doesn't know us. We don't hate anybody because of religion or color. I teach my kids to love everybody."
Julie Zauzmer contributed to this report.