Glenda Quiroz, 46, was struck by a pickup truck whose driver was possibly experiencing a medical emergency, police said.
Police said they believe the girl did not know the man.
Something caused him to run away, and no sexual assault occurred, Fairfax County authorities said.
The gang has been tied in recent months to homicides in Montgomery, Fairfax and Prince William counties and a surge in other crimes.
Police have opened an internal investigation into the flag, which shows a skull and crossed guns.
Chukwuemeka Ekwonna could face life in prison if convicted.
Police said the disappearance of Miguel Angel Ruiz Carillo, 18, might be gang-related.
Police said drugs may have played a role in the double homicide in Fairfax County.
Employees of the Department of Public Works have been authorized to take down any they come across.
