I only indirectly know of an Italian guy who was involved in the 80s in a football-related riot between two different supporters factions, where one young man ended up being killed by a knife wound.
He was indicted together with half a dozen of other supporters who joined that fatal fight: once the investigation started, it was a clear that one or more of them would have given an exemplary sentence and eventually would have served a very long sentence for homicide.
In order to avoid lengthy and expensive criminal proceedings and eventually going to jail for a very long time, he promptly bid farewell to all his friends and family and went to Marseilles by night train to enroll in the Foreign Legion (apparently this was advised/recommended to him by someone in the Police itself, at the time).
He spent there approximately a decade, being also involved in missions in Central America and Africa, and for that time nobody heard of him, not even his aging mother (I do not recall if he ever telephoned home).
After his time in the Legion, thanks to the new identity granted by his newly issued French passport, he settled somewhere in Southern France and returned to Italy at first only for brief periods (in order to meet his mother), and subsequently for longer extensions of time.
He had become extremely quiet and soft-spoken and never mentioned anything particular about his time in the Legion, except for the occasional non-descriptive bits with his closest relatives.
As far as I know, the “previous” person, with the relevant identity, citizenship and ID documents, just became untraceable under Italian law (like when someone disappears without leaving trace, a will or a suicide note).
The last time I heard of him — many, many years ago — he had moved permanently back to Italy and had joined an agency for the personal security of Italian VIPs.