Roger Macon, the police chief of the Fort Worth suburb of Saginaw, made the statement after officers exercising a search warrant removed more than 100 items from the home of Alanna Gallagher's parents, the Fort Worth Star-Telegram reported Tuesday.
"As with any criminal investigation, each of the people closest to the victim is being considered, and their actions investigated," Macon said.
The girls' partially nude body was found in a black trash bag wrapped with duct tape July 1 after she disappeared earlier in the day while playing outside.
The bag had been placed under a tarp near a curb on a residential street less than a mile from the girl's house.
Her cause of death has not been released by the Tarrant County medical examiner.
The chief said investigators had not found any evidence the girl or her two siblings were mistreated in the home.
Police say Miles McDaniel, who lived with Alanna's parents, Karl and Laura Gallagher, also is not considered a prime suspect. Laura Gallagher wrote on her blog that she and her husband were in a "polyamorous" relationship with McDaniel, who is listed in the child's obituary as one of her parents.