I don't know if he is smart enough to realize that even if the death penalty is brought back, it would not benefit him (since international law prohibits retroactive application of stricter punishments to the disadvantage of the sentenced). Well, if he commits another murder after the death penatly is reintroduced, he could still be executed, but it's extremely unlikely given his age (77) and general state of health.
He probably supports them because many of its supporters want to bring back the death penalty which is what he wants.
I guess he supports UKIP just because he's dumb and xenophobic.
Given he personally wants it could it be posed as to his advantage?