The Orlando nightclub massacre renews arguments over who should own high-powered weapons

The mass shooting that erupted at a gay nightclub in Orlando and left 50 people dead is renewing arguments about who should be able to own high-powered weapons in the US.

The suspected gunman, 29-year-old Omar Mateen, had an AR-15 assault rifle and a handgun during the attack at Pulse early Sunday morning.

FBI officials say despite Mateen being investigated three times since 2013, he was able to legally purchase the guns used in the massacre.

When asked why Mateen was still able to obtain his weapons despite his past run-ins with federal authorities, retired Army intelligence officer and Stetson University law professor, Charles Rose III said it came down to the FBI's lack of concrete action against Mateen.

"If the FBI had identified the shooter as someone with possible terrorist links, the ability to purchase a firearm might have been taken from him," Rose said in a conversation with Business Insider.

Rose said, if nothing else, the shooter "might have at least been higher on a watch list."

He notes that "fall-out" occurs when authorities have "actionable intelligence, but not enough to detain [a person] based upon probable cause."

Rose said the root of the problem is in the way the US handles domestic terrorism as "a criminal, rather than a military activity." In doing so, Rose added, the suspect retains their Constitutional rights.

"Someone can assert their association with ISIS under the freedom of speech umbrella and say they're going to do something, but until they do it, they have all protections afforded to them under the law," he said.

Rose added that if one's association with a terrorist organization resulted in them being classified as an "enemy combatant, or a partisan under the Geneva Convention," suspects would be stripped of their Constitutional protections. He says the reason why that is not the case is "strictly political."

Gun-reform advocates have pushed for stronger restrictions on certain types of gun-buyers in recent years, but conclusive legislation on the matter has been fleeting.

In January, President Obama revealed new executive actions designed to narrow the "gun-show loophole" by requiring firearms dealers to issue tougher background checks on prospective buyers.

Obama's actions also expanded the Bureau of Alcohol, Tobacco, Firearms, and Explosives, aimed to improve mental-health treatment, and sponsored new research into gun-safety technology.