"Forensic tests have confirmed that a white Fiat Uno collided with the Mercedes"
That bit never rung true to me. Have you ever driven a Fiat Uno? Tin foil wrapped over a bamboo frame is what it feels like. And that is supposed to have caused a Merc to have a crash, and then driven away?
No way!
Even if it had happened, nobody would have tried to do it deliberately. It owuld have been suicide.
