A man sacked from an Oklahoma food processing plant beheaded a woman with a knife and was attacking another worker when he was shot by one of the bosses.
Police in the Oklahoma City suburb of Moore are waiting for Alton Nolen, 30, to regain consciousness to arrest him over Thursday's attack.
They have asked the FBI to help investigate after co-workers at Vaughan Foods told authorities that Nolen had been trying to convert several employees to Islam.
Sgt Jeremy Lewis said Nolen severed the head of Colleen Hufford, 54, then stabbed Traci Johnson, 43, a number of times before Mark Vaughan, the company's chief operating officer and also a reserve sheriff's deputy, shot him.
"This was not going to stop if he didn't stop it. It could have gotten a lot worse," Sgt Lewis said. "The threat had already stopped once we arrived."
The horrific attacks took place after Nolen had been sacked in a building housing the company's human resources department. Police said he then immediately drove to the main entrance of the business.
A Vaughan spokeswoman said the company was "shocked and deeply saddened" by the attack.
Moore police have asked the FBI to look into the man's background because of the nature of the attack, which follows a series of videotaped beheadings by Islamic State (IS) militants.
FBI Special Agent in Charge James Finch said the motive for the attack had not been determined but that there was no reason to believe there was a threat to anyone else.
A law enforcement source familiar with the investigation said while there was an indication that Nolen was a Muslim convert and was trying to convert others, there was so far no connection to terrorism or evidence of any worrisome travel.
The official said Nolen had a Facebook page that was of potential interest to investigators but that "there doesn't appear to be any nexus to terrorism right now".
Ms Johnson and the suspect were taken to hospital and said to be in a stable condition.
Oklahoma Department of Corrections records say Nolen served time in prison and was on probation for assault and battery on a police officer. He also was convicted of cocaine possession with intent to distribute in 2011.
The records show Nolen has what appear to be religious tattoos, including one referencing Jesus and one in Arabic that means "peace be with you".