BUFFALO, N.Y. - The fatal shooting of a Buffalo man by a city cop has re-focused attention on one of the most critical decisions a police officer makes: Shoot? Don't shoot?

"If they make any type of decision to use deadly physical force, it is absolutely the last resort,” says Steven Padin, a retired Buffalo officer and firearms instructor at the Erie County Police Academy.

Padin's job is train officers with the life or death decision of when to use deadly force. He did not talk about the early Wednesday morning shooting of Rafael 'Pito' Rivera. That remains under investigation.

But 2 On-Your-Side did ask Padin questions based on what city police officials and sources have told us about the incident.

Rivera has been repeatedly described as armed and refusing to drop a 9mm gun in his hand.

Padin says that scenario is a red flag.

"If an officer is repeatedly telling somebody to drop a weapon that they have in their hands and the person is refusing to do so, then that is a sign that something bad is about to happen right here,” says Padin.

He also says it is not necessary for an armed person to point a weapon at someone for the officer to consider using deadly force.

"Even if they're not facing the officer because, keep in mind the officer's job is not only perserve their life but also the public's," says Padin.

And while it is common for officers to tell someone who is armed to drop their weapon, it is not required before using deadly force.