Who's to say he didn't have control over his actions?
In the same way you assumed he couldn't be reformed I was assuming the mental defect caused this.
He is obviously mentally unstable but you can't prove that he was at the time of the murders. For all we know the experience of committing those heinous crimes could have drove him mad or being locked in confinement knowing he is most likely going to die could have. We can't prove when or if an illness caused his actions.
Yeah, we can't, which is why imo he shouldn't be executed. It's better to keep a guilty man alive than risk executing an innocent person [in this case its not guilty vs innocent, but mentally stable crime vs unstable crime, just saying this before someone pointed out the innocent person in the analogy did kill]
There's also the point that prisons are supposed to be used to reform people and turn them into productive members of society. I highly doubt this guy can be reformed and made productive.
Prisons are only to reform on paper, no one expects reformation from prison, which is why he should be in a high security mental health facility.