Avram, actually according to a recent study most murders are executions. The murderer decided that the victim did something that makes him deserving of death. According to the US DOJ Bureau of Justice Statistics “Almost half of the victims died in fights with the offender arising from property disputes, domestic arguments, insults or feuds. An estimated 11 percent were involved with the killer in illegal drug activities and 12 percent were collaborating in other criminal activities with their killer.” The death penalty might well deter all but the suicidal. At any rate, they will never kill again.
Ubiquitin, one can kill even more with explosives. Criminals can get either or make it without any problem.