FBI agents work the scene at the Armed Forces Career Center in Chattanooga, Tennessee, July 16, 2015. The shooter used an AK-47-style assault weapon, CNN reported. Reuters

Mohammod Youssuf Abdulazeez, the shooter who reportedly killed four Marines on Thursday, used an AK-47-style assault weapon with a 30-round magazine in his attack on two military centers in Chattanooga, Tennessee. The attack on the two centers -- an Armed Forces Recruiting Center in a local strip mall and a Naval Reserve Center roughly seven miles away -- also left three injured.

The type of weapon used was reported by CNN. Semi-automatic rifles, like the one Abdulazeez used, are designed for rapid fire and combat use, maximizing the potential damage they can cause. A semi-automatic rifle was also used in the 2012 shooting at Sandy Hook Elementary School in Connecticut, which left 20 children and six adult staff members dead.

"He had a big, huge, high-powered rifle," Gina Mule, who was opening up her restaurant nearby the Armed Forces Recruiting Center, told CNN. "And he was unloading shots right into the recruiters. There had to be 20 to 30 shots."

The availability of assault weapons and high-capacity magazines has been a frequent public policy debate after mass shootings, with Second Amendment advocates arguing that the weapons are a constitutional right, while opponents push for local and federal bans on the guns that they say are used only for violence. Advocates of gun rights suggest that a greater presence of weapons would help to dissuade or stop attacks, potentially minimizing the number of fatalities.

"When the military switched over to this assault weapon, the whole context changed," said Tom Diaz, formerly of the Violence Policy Center and author of "The Last Gun," a book about the militarization of civilian firearms, as the New York Times reported. “The conversation became, ‘Is this the kind of gun you want in the civilian world?’ And we who advocate for regulation say, ‘No, you do not.’”