Who can explain the workings of a deranged mind? Sometimes it's the colour, politics, or the religion of the victims which gives us some clues. The Christchurch, NZ, mosque attacker, whose shooting left 51 dead, didn't need to shout anything. His gun did the talking for him. Same thing with the Norwegian attack, van bomb and shooting at a Labour Party youth camp where 81 died, the violence did the talking.
I believe these killers have slipped into lunacy before they carried out their attacks. Their deeds were hardly the acts of rational people. I also believe that such people are so dangerous that they should be held securely for the rest of their lives.