Authorities said on Friday that it was still too early to know what motivated a gunman who killed eight employees at a FedEx facility in Indianapolis and wounded several others before taking his own life.

The shooting - the latest in a spate of recent mass shootings across the United States that has reignited a fiery debate over gun violence - unfolded at a FedEx operations center near the Indianapolis International Airport after 11 p.m. local time on Thursday night, police said.

The incident, which lasted only a couple of minutes, was already over by the time police responded to the scene, Craig McCartt, the Indianapolis police department's deputy chief, told a news briefing on Friday. Witnesses described a chaotic scene, as the gunman opened fire in the parking lot before entering the facility and continuing to fire.

Officers found the suspect dead inside the facility of an apparent self-inflicted gunshot wound, along with four victims. The other four victims were outside.

FBI Indianapolis Special Agent in Charge Paul Keenan said it would be "premature to speculate" on the gumnan's motive. Authorities have not yet publicly named the suspect or any victims, though McCartt said police "have an idea" about the gunman's identity.

A FedEx employee, Levi Miller, told NBC's "Today Show" he saw a "hooded figure" holding what appeared to be an AR-style semi-automatic rifle who shouted and opened fire outside the facility.

"I thought he saw me, and so I immediately ducked for cover," he said.