First came word of a woman stabbed. Then screams. Then gunshots.

But the full story of Thursday's gruesome beheading at an Oklahoma food processing plant -- especially why it happened -- is still waiting to be told.

One day later, there are tears for Colleen Hufford, the 54-year-old woman whose head was severed. There are prayers for 43-year-old Traci Johnson, who is in stable condition at a nearby hospital for treatment of "numerous wounds," according to police.

And there are questions about 30-year-old Alton Alexander Nolen, the man who authorities say attacked them both and might have gone after more people if not for the company's CEO, also an off-duty reserve sheriff's deputy, who confronted and shot him twice.

Answers may come from Nolen himself. As of 6 p.m. (7 p.m. ET), he was "coming out of a sedation" at a hospital and investigators planned "to attempt to begin interviewing him as soon as he was coherent enough to understand what was going on," according to Sgt. Jeremy Lewis of the Moore Police Department.

Alton Alexander Nolen is seen here in a mugshot from a 2010 arrest in Logan County, Oklahoma.

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Here's what they do know:

The attack happened very soon after Nolen learned he'd lost his job.

Nolen had been incarcerated until March 2013, for possession of a controlled substance, escaping confinement and resisting an officer.

And he had been trying to convert co-workers to Islam.

Lewis also said there may be other information about Nolen's past, that he could not reveal, that might help explain the incident, and that the FBI had been called in to dig deeper into Nolen's background.

"Once we started investigating this initially, and started finding some of the things that he had been involved in, some of the things that he had been saying, we immediately contacted the FBI and got them involved," Lewis told CNN's Erin Burnett.

CEO/reserve sheriff's deputy stops attack

The large, rectangular Vaughan Foods processing plant looks like many others from the outside: a no-frills design, nondescript front entrance and loading bays out back.

But Friday, there was nothing normal about it. Police cars were everywhere, and uniformed officers walked the property. Some citizens stood outside watching, putting their arms around each other and trying to make sense of the horror the day before.

Some of this drama could be heard in a 911 call released Friday by the city of Moore.

It starts with a man yelling out, "Shut the doors," before calmly turning his attention to a 911 dispatcher.

"We have someone attacking someone in the building," he says.

The initial violence happened near the Vaughan Foods plant's main entrance, but didn't stop there. According to a 911 call, the suspect went through the front office, to the shipping office, then over to a customer service office.

Did he know who he was attacking? Not according to Lewis, who said the suspect used a knife -- which, otherwise, would be used in the processing of produce at the plant -- to randomly inflict bloodshed.

"He wasn't targeting anyone, wasn't going specifically after them," the police spokesman said. "It appears they were just in his way as he came in."

The onslaught's end could be heard on the 911 call, when the caller's steady voice was interrupted.

"Can you hear this in the background?" he tells the dispatcher. "And that, that's a gunshot."

Three shots rang out in total, according to the caller.

There's no indication that the suspect, Nolen, was armed with anything other than a knife. Of course, no one knew that at the time: They only knew that someone had entered their workplace, beheaded one woman, then attacked another.

Mark Vaughan -- who besides being his company's CEO has been a reserve deputy with the Oklahoma County Sheriff's Office since June 2010 -- "didn't hesitate" after learning that there was a killer on the loose, Sheriff John Whetsel said in a statement.

Instead, he confronted and twice shot Nolen, who is now hospitalized in stable condition.

"Without regard to himself or his safety," Whetsel said, "yesterday Mark Vaughan became a 'HERO' while doing the job he was sworn to do -- protecting others."

Beheading raises questions, but officials say no terror link

The idea that a man who's been trying to convert others to Islam ends up beheading someone is alarming enough, but perhaps even more given what has been happening in the Middle East.

The Islamist extremist group ISIS has made a name for its itself using such tactics, going so far as to record the beheadings of American journalists James Foley and Steven Sotloff as well as British aid worker David Haines.

And they've threatened more to come, especially if the United States and its allies continue to launch airstrikes at the group in Iraq and Syria. This has spurred concerns that ISIS sympathizers may similarly lash out against innocents in the West.

That said, it's not known if Nolen's religion had anything, at all, to do with what happened Thursday.

The FBI and other investigators, of course, could eventually find some sort of link or tie Nolen to others.

But that hasn't happened yet. As of Friday, all U.S. law enforcement officials said was that there are no indications linking the Moore attack to terrorism.

A spokesman for Oklahoma Gov. Mary Fallin, Alex Weintz, noted the governor had blocked Nolen from receiving parole in 2012, but said she "believes we need to let law enforcement do their job and not to jump to any conclusions before the conclusion of the investigation."