Dr. David Trask is the presiding hospital doctor over the case of schizophrenic man Danny Payton. Danny stopped taking his prescriptions, so Dr. Trask didn’t take Danny back into the hospital. When Danny was on a drive to calm himself, he still had hallucinations that drove him to kill Emily Milius from behind the wheel.
Dr. Trask was questioned and provided his account of Danny’s case. It was enough to prove after his mother Diane killed him that they both had ample opportunity to stabilize his condition before the murder. (L&O: "Mother's Day")