The "pony express" rider on the Suzuki motorcycle looked like hundreds of others who risk life and limb weaving in and out of central London's busy traffic.
When he was stopped at a road block last October, he produced a driving licence with an Italian name, a name that the traffic policeman wrote down and later, as a matter of routine, checked out on computerised police records.
To the policeman's surprise, the records showed that someone with exactly the same name - Antonio Ferdinando Carretta from Parma - was listed by Interpol as a missing person. Through Interpol, police in Parma were soon alerted to the "discovery".
The news that Ferdinando Carretta had been found in London provoked an immediate clamour in Italy, setting the clock back nine years to August 1989 when the entire Carretta family - Ferdinando, his father, Giuseppe, his mother, Marta, and his brother, Nicola - had all disappeared.
News of the family's disappearance first broke when neighbours and friends had alerted police to the fact that the family had not returned from their summer holiday in their mobile camper-van.
Through a popular TV programme, Has Anyone Seen This Person?, the holiday camper-van was later found in a Milan car-park, but the empty vehicle contained no information as to the family's whereabouts.
Investigators did not, at first, suspect foul play but tended to believe that the father, Giuseppe Carretta, might have absconded to a tropical paradise with his family and funds embezzled from the Parma glass company, Cerve, where he worked as an accountant. Despite denials from Cerve concerning any theft, the investigation had remained stuck at that point and on that theory until the zealous London traffic policeman intervened last October.
Rumbled by the traffic policeman and subsequently by Parma investigators and Italian journalists, Ferdinando Carretta opted to return to Italy last month, and was arrested on his arrival at Rome's Fiumicino airport. Since then, in testimony to a Parma investigating magistrate, Judge Vittorio Zanichelli, and in a dramatic television interview recorded in a London hotel before his return to Italy, he has revealed the mystery of the Carretta family.
He said: "On August 4th (1989), I took out my gun and shot both my parents and my brother . . . It was an act of total madness."
Ferdinando Carretta has told largely the same story in the television interview and to Parma magistrates. It is one that neatly ties up all the loose ends, perhaps too neatly.
Ferdinando says he killed his father because of a deep loathing for him. He deliberately provoked an argument with him on the night in August 1989 before the family, minus Ferdinando, were due to go on their camper-van holiday.
When the argument reached fever pitch, Ferdinando ran to his room and pulled out a Walther 6.3 revolver, bought in nearby Reggio Emilia some months earlier, and then ran back down the apartment hallway and shot his father.
When his mother, alarmed by the shot, came running out of the kitchen, he shot her, too, because she had witnessed the killing. Then Ferdinando sat down to await the return of his younger brother, Nicola (23), and shot him as he entered the family apartment.
Ferdinando claims he then dragged the bodies to the bathroom and dumped them in a bathtub full of water, where he left them for the next few days, remembering to change the water every now and then. On the night of the killings, he had gone out and moved the camper-van to a different car-park to give neighbours the impression that the family had left on their holiday.
After some days he wrapped each body in plastic sheeting and in the early hours of the morning carried them down the stairs from the second-floor flat and dumped them in the boot of the family Fiat Croma. Then Ferdinando drove the car to the municipal dump on the outskirts of Parma and, after encountering some difficulty in avoiding a courting couple, found some sandy soil in which he buried the bodies.
Following this, he left Parma in the family camper-van, abandoning it in a Milan car-park to avoid its being identified at border controls before setting off on a peregrination through Switzerland, France, London, Canada, New York and eventually back to London, a journey financed by £2,400 worth of cheques forged in his father's and brother's names.
Once he had returned to London, he settled down there and claims not to have left the English capital for the last nine years, during which time he has worked at odd jobs while occasionally claiming the dole.
So, all is resolved? Not quite. For a start, neither the bodies nor the murder weapon have yet been found. Ferdinando claims he threw the gun into a canal in Milan shortly after parking the camper-van, while this week he took magistrates to the spot where he buried the bodies. However, the burial ground has changed completely in the last nine years, during which millions of tons of refuse have been dumped on it, making it almost impossible to ever find the bodies.
Furthermore, investigators are perplexed by a number of factors. How come no one in the apartment building heard gun shots on the night of the killing? Is it possible, even in holiday-time August, that no one noticed Ferdinando carrying large and awkward objects down two floors of stairs?
Is it possible that Ferdinando was able, as he claims, to clean the flat so meticulously that no traces of blood or other body matter were found by forensic experts? Is it possible that at the height of the Italian summer no neighbour smelt the foul odours of the corpses?
If Ferdinando was anxious to confess his crime, as he now claims, why did he wait nine years to do so?
While investigators await answers to those questions, Ferdinando remains in preventive detention where he will be subjected to psychiatric tests to ascertain his mental stability.
Magistrates have ruefully pointed out that a court case based only on Ferdinando's confession and with no evidence of the dead bodies could even lead to his acquittal.
The mystery, it seems, may not have been resolved after all.