I am not in favour of capital punishment period. Is it going to prevent this man doing such a thing again? No, he'll be in jail for so long anyway that won't be an issue. Is it going to prevent anyone else doing such a thing? Probably not: this happens so rarely, and the person has to have such a peculiar drive to carry it off that it probably wouldn't affect any other potential perps. Is it going to help the victim or the children? Probably not: she had a relationship of sorts with him for many years and he is their father, after all. Even in your country, which has areas which support the death penalty, there is little reason to apply it for what is not a capital crime. You can't just make ad hoc exceptions for a particularly emotive crime.