Investigators believe he may be responsible for other incidents in the region.
He was supposed to be caring for his sister and two cousins. Instead he killed them, he told police.
The girls, two six-year-olds and a 9-year-old, were stabbed to death by an older brother of one of the children, Prince George’s County police said.
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.
Employees of the Department of Public Works have been authorized to take down any they come across.
