Eat them? Hrm, brings up my desires to attempt cannibalism (strangely, thats not a joke...)
Buuuuuttttttt.... Maybe you should try something slightly more subtle, like wearing the gas line in their homes so they die in their sleep... Or stage a robbery, so long as you have boddytight wear and FRESH latex gloves, a simple, stealthy knife would in the right place would be ideal...
Am I scaring you yet???
OOH! You could use my macabre landmine design, they are lots of fun, and leave nothing behind! So long as its constructed and concealed correctly, its dramatic yet untreaceable!
Urgh, I have too much time on my hands...