Authorities identified the gunman during the mass shooting on Friday as Gary Martin, 45.
He opened fire on Henry Pratt Co., in the suburbs of Chicago, in Aurora, firing at terrified employees before engaging in a fight with police officers.
The five employees who died in the shooting were men, the police said. The gunman was killed during an exchange of gunfire with law enforcement personnel, said Kristen Ziman, police chief of Aurora.
Martin, who worked in the company, was released the same day, police said. They did not provide any additional details as to why he was losing his job or the fact that he had been warned before the shooting.
"He was just shooting everyone"
He was "running in the driveway" with a gun with a green viewfinder, he said.
"As soon as I saw the green thing and heard the shots, we left," said Probst, who has been working at the factory for 40 years. "He started to open the room and he just shot everyone."
Probst said that one of the victims who escaped with a hemorrhage in his arm told him that the shooter "had become ballistic".
90 minutes of terror
About 90 minutes have passed since the shooting began to control the situation, the police said.
Calls to an active shooter began pouring in at 1:24 pm, and police arrived at the scene four minutes later and surrounded the scene, Ziman said.
When the police raided the 29,000 square foot building in search of the gunman, he shot them.
"Additional officers started arriving and were also shot," Ziman said. Five police officers were shot. A sixth policeman was injured in the knee and had to go to the hospital. All injured officers were shot in the first five minutes of their intervention, said Ziman, and their injuries are not life threatening.
Henry Pratt Co. describes itself as one of the largest manufacturers of industrial valves in the country. Mueller Water Products, its parent company, said it was providing assistance to affected families.
"Our hearts are with the victims and their loved ones, the first responders, the Aurora community and the entire Mueller family in this extremely difficult time," he said in a statement.
"Our main goal is the health and well-being of our colleagues, and we are committed to providing them with all the support they need, as well as their families."
A working group from the Kane County Sheriff's Office will investigate the death of the gunman, Ziman said.
Police use to identify victims
The authorities have not identified the victims during the last mass firing of the nation. But the police said that all the victims – employees and police – were men.
The governor of Illinois, J.B. Pritzker, who was sworn in a little over a month ago, thanked those responsible for enforcing the law.
"There is no way to get ready, there are no words for the kind of evil that deprives our neighbors of their hopes, their dreams and their future," he said. he said in a statement. "There are no words to express our gratitude to the families of the officers who were injured in the performance of their duties, because they reacted in a few moments to the most serious danger they may face. "
Mayor of Aurora, Richard Irvin, said mass shootings had become commonplace in the country.
"It is unfortunate that a cold, heartless delinquent is selfish enough to think that he has the right to live an innocent life." But we, as a society, can not let these horrific deeds become commonplace, "he said.
Shocked neighbor speaks outside
Martin's neighbor neighbor said he had moved into the apartment complex this summer. She said that she was not close to him but that the two were going to say hello to her by the way.
"He seemed very friendly, he said hello to a lot of people coming and going, I'm a little shocked, I suppose," said Mary McKnight. "I'm sad and shocked, and you never know."
Aurora is the second largest city in Illinois and has approximately 200,000 inhabitants.
Steve Almasy of CNN contributed to this report.