KNOXVILLE, Tenn. (WVLT) -- Vinson guard services provides the protection for Markman's, and they say the officer involved in the Saturday afternoon shooting is a state licensed armed guard.

It's a 2-day process to become an armed security guard, but in that time period you're supposed to learn all about the law.

But a local security expert says in this situation, the guard should never have intervened in a domestic dispute outside of the jewelry store.

"You're liable and accountable for every round that's discharged from that weapon, so again the best shooting is no shooting." says Edward Howell Jr., owner of Diligence Security and Patrol.

With a state certified trainer, he teaches his armed guards when to pull the trigger.

Howell says "our officers are taught that anything that happens on-sight, the property their protecting, the first thing you do is call 9-1-1, get the police in route."

But he says the guard posted at Markman's jewelry store on Kingston Pike, should not have left his post Saturday for a domestic dispute outside.

Howell says "that person can be beating someone up but you stay out of it because you're there to protect that building and that personal property for the company you're working for."

The state requires security officers to have the proper credentials.

Howell says "the state requirement is 16 hours of class time and that includes unarmed and armed."

It's 12 more hours of training to be an armed security guard in Tennessee, including education on the legal limitations on the use of a firearm and completion of a target course.

Howell says "unless there is inevitability of you being hurt or someone else, which is called defense of a third person, then you are not allowed to use deadly force."

And with that deadly force in hand for armed guards, Howell provides more extensive training for his guards.

He says "we want our students, our security officers to be the best they possibly can be for the simple fact that one little mistake that you make can ruin you, can ruin a company

Edward Howell says a big rule for his guards, is to never leave your post, and to always first call police.

Vinson Guard Services says they too go above and beyond in their training.

The state requires re-certification of armed guards every 2 years, and they say they do re-certification classes every 6 months.