The killer's ex wife has been found dead. She had a restraining order put on the guy, and she worked in one of the stores where he went to kill people, the other victims were her co-workers. She had lived with the dood for 18 years before moving out last year, got a restraining order in april.
About the guns, the gun laws were tightened up after the latest school shooting. Age limit was raised and you have to go through a more elaborate screening test.
Edit: Looks like the dood killed himself now as well.