Below is a link to a Wiki page of murdered boxers. I'm sure there were others - or even fighters who died too soon.
So here's two of them.
Julian Letterlough served 7 years in prison, got out & started a boxing career shortly before his 29th birthday.
He racked up 15 wins (all kayos) & 1 draw before challenging Julio Cesar Gonzalez for a regional title. It was an absolute war with Gonzalez down thrice & Letterlough twice.
Gonzalez won & went on to lose to Roy Jones, then pick up the WBO & IBF titles before fading away.
Both would be dead at the age of 35.
Letterlough from a bullet to the back of the head by a drug mob gangster (as he left a restaurant with his wife) while Gonzalez died seven years later in a car crash.
Anyway, for the anoraks among you, here's the WIki page of murdered boxers
https://en.wikipedia.org/wiki/Category:Murdered_boxers