The Oklahoma medical examiner's office says all five members of a Broken Arrow family killed last week died from multiple sharp-force injuries, and police have said two knives and a small hatchet were found at the scene.

Medical examiner spokeswoman Amy Elliott said Monday that the manner of death is homicide for each of the five members of the Bever family.

Eighteen-year-old Robert Bever is accused in a booking document of five counts of first-degree murder and a count of aggravated assault in the Wednesday night attack at the family home. Prosecutors say they plan to also charge Bever's unidentified 16-year-old brother as an adult in the case.

Formal charges have not yet been filed.

The parents and three siblings of the brothers were killed. A 13-year-old sister was wounded.