Steam them live.
Use beer instead of water.
Heat the kettle, use a mesh bottom to keep the crabs from swimming in the beer, wait until there's a good 'head of steam', quickly dump the crabs, liberally sprinkle the crabs with OLD BAY seasoning, jam the lid down quickly to stop the escapees .... Yum.
If there are any toxins in the backfin or claw meat ... the manner/choice of 'execution' wont make any difference. The yellow 'liver' (hepatopancreas) or 'tomalley' ... thats where most of the toxins will be concentrated, few eat the tomalley any more for this reason.