They may never know. A true mystery.
Victims were asked if they were Muslim before being stabbed and he shouted Allahu Akhbar over and over, but this one is a real head scratcher.
FBI Still Baffled Over Motive in Minnesota Mall Stabbing Attack Claimed by ISIS
The motive seems pretty clear to me. Dude was committing Jihad.
What? How in the world can anyone claim Islam was the motive when the all the guy did was saying he was with ISIS, asked victims if they were Muslim and shout Allahu Akhbar at people? You jump to conclusions too easily.
Ummm, pretty simple, if you understand the topic.
Upon further contemplation, I must revise my statement. He may not have been commiting Jihad, however, it is pretty obvious that he THOUGHT he was. The following explains why I say this:
" ...unbelief in itself is not the justification for war. These jurists therefore maintain that only combatants are to be fought; noncombatants such as women, children, clergy, the aged, the insane, farmers, serfs, the blind, and so on are not to be killed..."
Jihad - Wikipedia
However:
"Many Islamist extremists have co-opted “Allahu Akbar” as a war cry."
What does 'Allahu Akbar' mean and why do terrorists shout it?
So, yeah, maybe he wasn't actually committing Jihad, but it's pretty clear that he likely thought he was.