As there have been quite a few incidences of a pilot intentionally crashing a plane, It would be interesting to see if the ratio of mass-murdering pilots to pilots is larger than mass-murderers vs the adult population.
This would have to be adjusted to the fact that most people is not usually in a position to easily kill this many people, while pilots are in a mostly daily basis.
You could check against bus drivers for instance.
But mass-murdering pilots wouldn't necessarily use their planes to mass murder so that rules out pilots as a distinctive group. /armchair-whatever