It wasn’t a murderer, but in 1984, Gary Plauche killed Jeff Doucet while Doucet was being transferred from California to Baton Rouge for trial. Doucet had sexually abused and kidnapped Plauche’s son (who was recovered unharmed). Plauche was tipped off to the time and date of the transfer by a television station employee. Plauche waited in the airport, and when police came by with Doucet, Plauche shot Doucet in the side of the head.
I remember seeing the news report at the time, and remembered just enough that I was able to find the details via google.
Plauche was given a seven-year suspended sentence with five years’ probation and 300 hours of community service. He did not serve any time in jail.
Larry Flint was shot near the courthouse on his way to trial. There is definitely a risk to people accused of certain crimes. When in police custody, the government has a duty to protect them, thus the vests.