The Torah position is very clear with people who commit capital offences.
Justice needs to be served in a moral society. We have no ability or right to forgive him – that is between him and G-d. On the contrary, putting him to death is part of his atonement process.
However, there are also rules as to how he is to be treated. He is still a Jew and he may not be degraded. Before being put to death he is told to repent and reminded that if he does so he STILL MERITS A PORTION IN OLOM HABA.
Remember, Kayin killed Hevel in cold blood and his Tshuvah was accepted.
Also to one of the previous posters who used the word ‘Yimach Shmo’ about Aron. I once heard that however low a Jew has sunk, (and I think Aron, if he is sane has hit the bottom) those words are never allowed to be used about Jews aside for two individuals who were Meshichei Sheker (one was Shabsai Zvi, the other is probably not a good idea to post on a public forum)