Police in Oklahoma say they have turned to social media posts for clues about the motive of a teenager accused in the stabbing deaths of his parents and three siblings during a late-night attack that left bodies strewn through the family's home.

A booking document filed by police in the Tulsa suburb of Broken Arrow accuses Robert Bever, 18, of five counts of first-degree murder and a count of aggravated assault in the attack Wednesday night.

Bever's 16-year-old brother also was being held. Because he is a juvenile, officers have not released his name or announced charges against him. Broken Arrow Police Cpl. Leon Calhoun said both brothers were cooperating with the investigation.