"Everybody surrounding the two children are part of the questioning," she said.
As for the mystery man with the long ponytail who may have seen the girls before they were shot, Brown said her agency has received a lot of phone calls but authorities have not been able to find this "witness" or "person of interest."
He is described as an American Indian, about 6 feet tall, with black hair and a pony tail. He was driving a white Ford or Chevrolet single cab pickup with chrome stripping and an Oklahoma license tag. A composite drawing of the man was released last week.
"We don't know where he is right now," she said. "If we knew, we'd be talking to him right now. I don't know if he's afraid to come forward," Brown said. "But he doesn't need to be."
Investigators say the man was seen standing near the pickup around the time and place the girls were shot.
"It's paramount we find this person as quickly as possible," Brown said.
Contributing: The Associated Press