> Do we know if air marshals were on the flight? Sample size is too small to draw conclusions.

I assume that they weren't. If we can't afford to put air marshals on every flight, that's a weakness. (It may be a reasonable weakness given the cost, but it's still a weakness.)

Note that the deterrence argument of air marshals assumes that folks who are willing to die are unwilling to spend time in prison. That may be true, but I'd like to see some evidence. (The deterrence argument is how you get from "air marshals on x% of the flights protects more than x% of the flights".)

There are always other passengers on passenger flights.