The reason I hold for capital punishment is my firm belief that forgiveness of any trespass is the sole privilege of the victim. The Lord can forgive all, however, we can only forgive that which has been done against ourselves. A victim of murder can no longer forgive their killer thus justice demands that we require repayment for that which was taken be exacted. A life once taken requires a life forfeited in return. No friend, relative or human judge can remove this debt!
I agree with you on all points but one: even G-d cannot forgive transgressions against another human being, only the victim can. That is why murder is so unforgivable - because that is literally true. He can and does forgive for transgressions against His law. Keep in mind that I am Jewish, and thus bring my faith’s P.O.V. to this question. On Yom Kippur, our Day of Atonement, we are required to ask forgiveness of those we have wronged in the past year, and show some to those who have wronged us...because if we are asking G-d to forgive us for sins against Him, we have to take the first step.
As for K.G., kudos to him for letting go of the hatred that would be natural in these circumstances for anyone. I’m not sure that I could do that. Note that I believe that he can forgive this animal for the emotional harm that he, himself, suffered.