Sadism is kin to masochism. His desire to be punished is demonstrated by the horror of his actions. A quick, painless death is warranted.
Let's compromise. Toss him into a large vat of molten iron.
>> A quick, painless death is warranted.<<
Do you think what he did to the baby was pain free? No, he should be hung by his gentiles until they fall off, then fed into a wood chipper feet first.