Gracjan Bogucki
Gracjan Bogucki voted up Anonymous' answer

Even crimes involving people suffering from psychosis have a motive- just not one everyone can understand.

The Planned Parenthood terrorist, Robert Dear, had a motive of extremist right wing ideology.  These terrorists seemed to have militant Islamic ideology.  Dylan Roof was a terrorist with white supremacist ideology.  The core philosophies or religions of terrorists often form … Read more

Gracjan Bogucki
Gracjan Bogucki voted up Walt O'Reagun's answer

You need a motive for killing even 1 person.

IMO ... They were planning on getting away with it.  The only reason for destroying their electronic "footsteps" would be to prevent the authorities from tracking them down afterwards.