even in those cases there is still the question if a person is capable of guilt, because noone with a normally working psyche would entertain the thought of such deeds. i would support up to unlimited detention in a high-security psychiatric care facility (in such cases probably with a minimum stay of 10-15 years), which gives the population the needed security and the perp at least a chance to become a valuable member of society again. capital punishment is just a +1 to the bodycount.
I had more the human aspect than the legal definition in mind when i thought about guilt.
i’m sure he knew it was illegal, but that knowledge often doesn’t help or just steps into the background when mental strain and pressures just get strong enough. I’m convinced that with working mental health care (and a social safety net thats worth a damn) a lot of those violent outbursts could be just not happening.
in the same vein i think that even if such an outburst happens, it is not per se indicative of repeat offenses, if the offender actually receives rehabilitation and not simple punishment (especially at such a young age) - in contrast to a career criminal who is used to the “life style” or someone who has a long list of violent behavior.
ETA: had time to read the complete article now. his was a crime of anguish and pain, who did not get help even when it was blatantly obvious what was happening inside of him.