But I promise you that if you shoot him only once and the EMS guys save him, you WILL be hearing his side of the story in a courtroom.
All the more reason to only have one side of the story in court...yours!
Really guys, how about whether it can be proven, and whether or not you would be convicted, shooting someone to prevent them from subsequently testifying against you in a criminal or civil trial is murder!
The only reason you are justified in shooting some one is to protect yourself or another person from an imminant threat of death or serious physical injury. Anything else is not justified. You could be justified with your first two shots, and not your third. If you think you need two shots to stop the threat, and a third to prevent the guy from suing you, and you shoot three times, you've committed murder.
(Until the Courts threw out New York's death penalty due to a technicality, killing someone to prevent them from acting as a witness was death elligible.)