Air marshalls justified in shooting Alpizar?

Now that a couple of days have passed, a lot of people are wondering wither the air marshalls were justified in shooting Rigoberto Alpizar. Eyewitess accounts seem to directly contradict the official reasons given for the shooting:

One passenger said he “absolutely never heard the word ‘bomb’ at all” during the uproar as the Orlando-bound flight prepared to leave Miami on Wednesday.

Federal officials say Rigoberto Alpizar made the threat in the jetway, after running up the plane’s aisle from his seat at the back of the jetliner. They opened fire because the 44-year-old Home Depot employee ignored their orders to stop, reached into his backpack and said he had a bomb, according to authorities.

It is hard to say exactly what I would do in that situation without actually having been in that situation, of course. But I’ve gotta believe that there was another resolution besides shooting the guy in the back. Surely one of the marshalls should’ve been able to tackle they guy.