I modified my suggested license because of this shooting...

http://www.tampabay.com/news/publicsafety/crime/at-party-before-shooting-accused-killer-of-police-officer-said-he-was-in/2222102

Suspect in police officer's killing said he was in a mood to kill, records show

"He's showing me the gun and he's showing me all the spots where — if he would shoot somebody, where it would kill them and where it wouldn't," Ashton Colvin, 26, told detectives after the shooting. "At the time, I didn't think anything of it because I thought he was just drunk and talking crazy."

Several people who knew Parilla, who has an extensive criminal record that includes 30 felony charges, told police that smoking synthetic marijuana had ruined his attempt to go straight after prison.
"Once he started smoking the spice, his whole attitude and life seemed to deteriorate," one neighbor at Glen's Eureka told police.

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I added that anyone under the influence should lose their guns and license:

People Control, Not Gun Control

This is my generic response to gun threads where people are shot and killed by the dumb or criminal possession of guns. For the record, I grew up in the South and on military bases. I was taught about firearms as a child, and I grew up hunting, was a member of the NRA, and I still own guns. In the 70’s, I dropped out of the NRA because they become more radical and less interested in safety and training. Some personal experiences where people I know were involved in shootings caused me to realize that anyone could obtain and posses a gun no matter how illogical it was for them to have a gun. Also, easy access to more powerful guns, guns in the hands of children, and guns that weren’t secured are out of control in our society. As such, here’s what I now think ought to be the requirements to possess a gun. I’m not debating the legal language, I just think it’s the reasonable way to stop the shootings. Notice, none of this restricts the type of guns sold. This is aimed at the people who shoot others, because it’s clear that they should never have had a gun.

1.) Anyone in possession of a gun (whether they own it or not) should have a regularly renewed license. If you want to call it a permit, certificate, or something else that's fine.
2.) To get a license, you should have a background check, and be examined by a professional for emotional and mental stability appropriate for gun possession. It might be appropriate to require that examination to be accompanied by references from family, friends, employers, etc. This check is not to subject you to a mental health diagnosis, just check on your superficial and apparent gun-worthyness.
3.) To get the license, you should be required to take a safety course and pass a test appropriate to the type of gun you want to use.
4.) To get a license, you should be over 21. Under 21, you could only use a gun under direct supervision of a licensed person and after obtaining a learner’s license. Your license might be restricted if you have children or criminals or other unsafe people living in your home. (If you want to argue 18 or 25 or some other age, fine. 21 makes sense to me.)
5.) If you possess a gun, you would have to carry a liability insurance policy specifically for gun ownership - and likely you would have to provide proof of appropriate storage, security, and whatever statistical reasons that emerge that would drive the costs and ability to get insurance.
6.) You could not purchase a gun or ammunition without a license, and purchases would have a waiting period.
7.) If you possess a gun without a license, you go to jail, the gun is impounded, and a judge will have to let you go (just like a DUI).
8.) No one should carry an unsecured gun (except in a locked case, unloaded) when outside of home. Guns should be secure when transporting to a shooting event without demonstrating a special need. Their license should indicate training and special carry circumstances beyond recreational shooting (security guard, etc.). If you are carrying your gun while under the influence of drugs or alcohol, you lose your gun and license.
9.) If you buy, sell, give away, or inherit a gun, your license information should be recorded.
10.) If you accidentally discharge your gun, commit a crime, get referred by a mental health professional, are served a restraining order, etc., you should lose your license and guns until reinstated by a serious relicensing process.

Most of you know that a license is no big deal. Besides a driver’s license you need a license to fish, operate a boat, or many other activities. I realize these differ by state, but that is not a reason to let anyone without a bit of sense pack a semiautomatic weapon in public, on the roads, and in schools. I think we need to make it much harder for some people to have guns.