I think that the terrorist was trying to transport bomb making materials when something went wrong. He stopped the SUV, turned on the hazard lights through shear force of habit, and fled.
There was a man seen running from the scene. Why would he run if he knew he enough time to get away? Also, two clocks were found in the truck. This suggests that he intended to make more than one bomb.
It happened less than 24 hours ago. Let's see if I'm right.