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.



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.



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.



The dead include his parents, David Bever, 52, and April Bever, 44 .



Police had said Thursday that the emergency call was silent.



A neighbor of the family, Matt Jacobsen, on Friday described the 16-year-old as a follower, not a leader, and "nerdy," given his interest in computers and technology.

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