(CNN) -- [Breaking news update, published at 12:30 p.m. ET]
Police in Aurora, Illinois, have released the names of the five Henry Pratt Co. employees who were killed in Friday's shooting:
• Clayton Parks of Elgin, Illinois. He was a human resources manager.
• Trevor Wehner of DeKalb, Illinois. He was a human resources intern and a student at Northern Illinois University
• Russell Beyer of Yorkville, Illinois. He was a mold operator.
• Vicente Juarez of Oswego, Illinois. He was a stock room attendant and fork lift operator.
• Josh Pinkard of Oswego, Illinois. He was a plant manager.
The gunman, Gary Martin, 45, shot several of the men at a meeting during which he was being fired, Aurora Police Chief Kristen Ziman said Saturday. At least one of the slain men was found on another level in the building, she said.
Martin was not supposed to own a gun because of a 1995 aggravated assault conviction in Mississippi, she said.
But he obtained one in Illinois in 2014. In January of that year, he applied for a firearms owner identification card, she said.
In March 2014, he applied to buy a gun from a dealer in Aurora. After a waiting period and passing a background check that did not involve fingerprinting, he bought the gun, she said.
Later that month, he applied for a concealed carry permit, and a fingerprint check led authorities to discover the Mississippi conviction, Ziman said.
The permit was rejected, and Illinois State Police sent him a letter demanding he voluntarily surrender the weapon, but he did not, the chief said. Investigators are trying to determine why he didn't surrender the weapon and whether law enforcement followed up with him to confiscate the gun.
"He was not supposed to be in possession of a firearm," Ziman said.
[Original story, published at 10:53 a.m. ET]
A man who was being let go from his job at a manufacturing business went on a shooting rampage Friday at his workplace in Illinois, leaving five workers dead and five officers and an employee shot and injured, police said.
The gunman, 45-year-old Gary Martin, was killed at the facility in an exchange of gunfire with law enforcement officers, some 90 minutes after the shooting started, Aurora Police Chief Kristen Ziman said.
All five employees who died -- and all of the injured -- were men, police said.
Martin opened fire with a Smith & Wesson handgun at the Henry Pratt Co. in the Chicago suburb of the Aurora, police said, shooting at terrified employees, some of whom frantically called 911.
One witness said the gun had a laser sight.
Martin then fired at the first arriving officers within a five-minute period -- possibly from a window -- hitting at least one outside, with others were struck inside the building as they entered, Ziman said.
The shooting then stopped as Martin apparently hid deeper within the 29,000-square-foot warehouse, setting off a hunt that ended with a final gunfire exchange about an hour and a half later, she said.
Martin was being let go Friday from his job at the company, police said. They did not give more details about why he was losing his job or whether he'd been notified before the shooting.
"What we're trying to determine right now is ... if it was premeditated in any way," Ziman told reporters Friday night.
'He was just shooting everybody'
An employee who survived the shooting told CNN affiliate WLS that the gunman was a coworker.
He was "running down the aisle" with a pistol that had a green laser sight on it, John Probst said.
"As soon as I saw the green thing and heard the shots, we left," said Probst, who's worked at the plant for 40 years. "He started opening up on the room, and he was just shooting everybody."
Probst said one of the victims who ran out with his arm bleeding told him the gunman "went ballistic."
90 minutes of terror
Calls about a shooter started pouring in at 1:24 p.m. CT. Ziman said she believes the slain workers were shot before officers arrived roughly four minutes later.
Arriving officers came under fire immediately, she said. Initial reports indicate Martin was firing from a window.
"All of the officers that were shot were (injured) within the first five minutes of arrival," Ziman said. "We believe (the officers' eventual entry) pushed the offender inside further," where he hid.
More first responders then entered the building with two missions -- one group searched for Martin, while the other tried to find victims, she said.
About 90 minutes after the incident began, Aurora officers and those from neighboring Naperville found the gunman. Martin shot at them, and they returned fire, killing him, Ziman said.
A sixth officer hurt his knee and needed to go to a hospital. All the officers' injuries and those of the surviving worker who was shot are believed to be not life-threatening, she said.
Henry Pratt Co. describes itself as one of the nation's largest manufacturers of industrial valves. Mueller Water Products, its parent company, said it's providing help to the affected families.
"Our hearts are with the victims and their loved ones, the first responders, the Aurora community and the entire Mueller family during this extremely difficult time," it said in a statement.
"Our entire focus is on the health and wellbeing of our colleagues, and we are committed to providing any and all support to them and their families."
A task force from the Kane County Sheriff's Office will investigate the gunman's death, Ziman said.
Police are working to identify the victims
Authorities have not publicly named the victims of the nation's latest mass shooting.
Illinois Gov. J.B. Pritzker, a Democrat who was sworn into office just more than a month ago, thanked law enforcement officials.
"There is no way to prepare. There are no words for the kind of evil that robs our neighbors of their hopes, their dreams and their futures," he said in a statement. "There are no words to express our gratitude to the families of the officers who were injured in the line of duty as they responded within moments to the gravest kind of danger that they can face."
Aurora Mayor Richard Irvin said mass shootings have become all too common in the nation.
"It's a shame that a cold and heartless offender would be so selfish as to think he has the right to take an innocent life. But we as a society cannot allow these horrific acts to become commonplace," he said.
Shocked neighbors speak out
Martin's next-door neighbor, Mary McKnight, told CNN she wasn't close with him but the two would say hi in passing at their Aurora apartment complex.
"He seemed very friendly. He said hi to a lot of people who came and went. I'm kind of shocked, I guess," said McKnight, who said she moved into the complex over the summer. "I'm sad and shocked, and you kind of never know."
Another neighbor, Jennifer White, told CNN affiliate WBBM she knew of him in part because she'd see him outside flying drones.
"He seemed perfectly fine. I've seen him out there with his drones," she said. "He always kept to himself."
Aurora is the second-largest city in Illinois, with a population of about 200,000 people.