I said I wasn't a parent. But I understand the impulse.
Justice served for who? For Sam? That's all well and good. What else has this driver done? Maybe he's just some idiot who had one drink too many one night and swerved at the wrong time. Maybe he's something more. Maybe the LVPD finding him would bring justice to other people in addition to your son.
There's a host of reasons why peace officers aren't allowed to work cases in which they have a personal interest.