Mystery of the man who fell to earth

In September 2012, a man in his twenties was found dead in Portman Avenue, a suburban street in west London. He had suffered horrendous injuries to his head and face, but had no identity papers on him - and no one had reported him missing. It soon became clear that the man must have fallen from a plane flying overhead on to the street below. Rob Walker has been following the police investigation into who he was and how he arrived on Portman Avenue.