TULSA, Okla. (AP) — The Oklahoma Medical Examiner's Office says four women found dead last week at a crime-plagued south Tulsa apartment complex each died from a gunshot wound to the head.

The office noted however that full autopsy reports are still pending for 23-year-old twin sisters Rebeika Powell and Kayetie Melchor, 33-year-old Misty Nunley and 55-year-old Julie Jackson.

Investigators have not said how the women knew each other or why they may have been targeted.

According to court records, police have identified a man who "at a minimum" witnessed the killings at the apartment.

That man is being held on unrelated charges in the Tulsa County jail. He hasn't been charged or arrested in the quadruple murder, though a judge increased his bond Wednesday from $11,000 to $250,000.