Emergency crews at the scene of the shooting.
CHICAGO, Illinois (CNN) -- Salvador Tapia returned to the Windy City Core Supply warehouse where he had been fired six months ago and killed six of his former co-workers, police said Wednesday.
Tapia, 36, was then shot and killed in the last of three gunbattles with police, said acting police superintendent Phil Cline.
"It appears he went throughout the supply warehouse shooting them. They weren't all in one section, they were in different sections of the warehouse," Cline said.
Most of the victims were in an office near the front door.
"There's really only one way out and one way in," Cline said. "Once he's inside and by that front door, he's got them cornered."
One man escaped with his hands tied behind his back. He met police outside the warehouse to describe the scene inside, Cline said.
"We're not sure why he didn't shoot that victim," Cline said, adding the employee was the only one who had been tied. "His hands were tied behind his back, but he was still able to get out."
Police tried to enter the building but Tapia came out and fired three shots at police, Cline said. Fire was returned. One minute later, Tapia came back outside the building and shot at police again.
Finally, after considering the injured victims inside, the Hostage Barricade and Terrorist team was "ordered to make an assault on the building."
Inside, authorities maneuvered through a maze of 55-gallon drums, crates and steel containers filled with engine parts. They found Tapia hiding behind the stored parts.
"He got up. He had the gun. They ordered him to drop the gun. He refused to drop the gun, and that's when the officer shot him," Cline said.
Tapia was found with a Walther PP .380-caliber semiautomatic pistol and at least one extra clip of ammunition.
The man who was bound by Tapia was the only person in the building who escaped. Another man was late for work and came to the scene while the crime was in progress, Cline said. He escaped without injury.
The only other employee of the company was stuck in traffic and not at work at the time.
Chicago police stormed the auto parts building at about 10 a.m. (11 a.m. EDT). Police were called to the scene at 8:37 a.m. (9:37 a.m. EDT) in an industrial area near the former Comiskey Park on the city's southwest side.
Four of the victims died at the scene, the other three, including the gunman, were taken to hospitals, police spokesman David Bayless said.
Tapia was fired for being "a poor employee," Cline said. He was late to work and often missed entire days. Cline said Tapia had at least a few telephone conversations with his former boss after he was fired.
It's unclear whether he had returned to the job site since his termination or met with his boss in person.
Tapia has been arrested 12 times, Cline said. He has an arrest record dating back to 1989, including counts of domestic battery, gun violations, aggravated assault and driving while intoxicated.
"The problem here is easy access to a firearm," Cline told reporters. "Here is someone who never should have had a gun that had a gun."
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