A profiler that they are interviewing on TV says he’s pretty sure that they already know who the shooter is. Didn’t say he himself knew.
It’s speculation, but maybe...
Those who were shot dead, were they together in a group or identified as knowing each other? Or no associated with each other?
This does not fit the typical terror profile for an attack - they are usually committed to, and resigned to, dying in the attack nor do they often break off an attack on their own. Once they make that decision that they will die they want to create as much death as possible.
There is no news saying he was confronted by anyone (although it’s early and still confused) - he entered a store - shot people - and left apparently on his own. Shootings like this are most often domestic or gang related (i.e. - target a specific person and shoot anyone else who happens to be in the way), but it could be sudden Jihad syndrome by another goofball. These are crazy times and we will eventually find out the who, what, and why.