MIDDLETON, Wisconsin — New details in the investigation into the Middleton, Wisconsin workplace shooter reveal he could not legally own a gun.

43-year-old Anthony Tong shot and seriously injured three coworkers Wednesday before officers returned fire.

Court records show Tong’s concealed-carry license was permanently revoked after a mental health incident 14 years ago in South Dakota. Tong told Sioux Falls police he kept guns and a large amount of ammo to protect himself. He said employees "talked badly about him."

While Tong’s motive for going on a rampage remains a mystery, Middleton police say one thing is clear, he shouldn’t have had a gun in the first place. The development comes as a shock to some in the community, but not Mark Moeller.

“People who do these things usually exist on the fringes,” he said. “Those guys are going to find a way to get guns.”

Court records show Sioux Falls police were called to Tong’s apartment in 2004 for a public safety concern. Police found a handgun, a rifle and hundreds of rounds of ammunition.

“(The) defendant was asked if he would consider shooting somebody else, to which the defendant would not answer…. Officers did feel at this time there was a danger to the public,” a Sioux Falls police officer stated. “(The) defendant made statements that there were people at work that were talking bad about him, but would not elaborate.”

“He had this mental health incident,” reiterated Middleton Police Chief Charles Foulke. “That resulted in law enforcement coming in and eventually having a court order to revoke his current CCW license.”

Foulke said from that point forward, he wasn’t eligible to legally carry or purchase a firearm. A law enforcement expert told TODAY’S TMJ4 that means Tong could not own a gun, even in his home.

“A federally licensed firearm dealer would have access to the fact that he was ineligible to purchase a firearm,” Foulke said.

Foulke said ATF investigators are having a difficult time finding where the gun Tong used at WTS Paradigm Wednesday came from and whose hands it may have passed through.