BROKEN ARROW, Okla. — 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.

Calhoun said Friday that the agency was still looking for a motive and was searching social media accounts that they believe belong to Bever. Those include community site Pinterest and a Facebook account.

On Pinterest, Bever showed an interest in Star Wars, the rock group Linkin Park and sports cars. A Facebook post lists him as a recent graduate of Citizens’ High School, which describes itself as providing “a home-school curriculum” for people hoping to earn a college degree.