ORLANDO, Fla. (AP) — A man who was fired from a Florida awning factory in April returned Monday with a semi-automatic pistol and methodically killed five people, then took his own life at the sound of an approaching siren, authorities said.

Orange County Sheriff Jerry Demings identified the shooter as John Robert Neumann Jr., a 45-year-old Army veteran who lived alone and did not appear to be a member of any type of subversive or terrorist organization.

The shooting began at about 8 a.m. after Neumann slipped through a rear door into the cavernous factory, an area larger than two football fields where awnings are stitched together for recreational vehicles. He paused at least once to reload.

“My experience tells me that this individual made deliberate thought to do what he did today. He had a plan of action,” the sheriff said. The gunman “had a negative relationship with” at least one of the victims.

“He was certainly singling out the individuals he shot,” Demings said, adding that most victims were shot in the head. Some were shot multiple times.

The motive remains under investigation. Deputies cordoned off the gunman’s mobile home in Maitland, north of Orlando, and were looking through any social media postings for clues. Neumann was honorably discharged in 1999 and did not have a concealed weapons permit, the sheriff said.

Arnie Boyd, who lives in the same trailer park, said Neumann wasn’t particularly social. “Every once in a while, he would ride his bike around and that’s it,” Boyd said. “We would speak only once in a while.”

The dead were identified as Robert Snyder, 69; Brenda Montanez-Crespo, 44; Kevin Clark, 53; Jeffrey Roberts, 57; and Kevin Lawson, 46.

Authorities had confronted Neumann once before at the Fiamma Inc. awning factory, when he was accused of battering a co-worker in June 2014. But after interviewing both men involved, deputies filed no charges, Demings said.

Neumann’s previous criminal record was otherwise minor — marijuana possession and driving under the influence — and the co-worker he allegedly beat up three years ago was not among Monday’s victims, the sheriff said.

Fiamma calls itself one of the largest manufacturers of awnings for camper vans, motor coaches and sport utility vehicles.

Shelley Adams said her sister, Sheila McIntyre, called her from the company’s bathroom during the shooting and kept repeating, “My boss is dead. My boss is dead.”

State and federal law enforcement officers converged on the awning business in an industrial park in Orlando shortly after 8 a.m. after a woman ran out and called 911 from a tile business across the street, said Yamaris Gomez, that store’s owner.

“All she kept saying was he was holding a gun and told her to get out,” Gomez said.

Officers were dispatched within 45 seconds and arrived two minutes later, the sheriff said. The FBI also responded, said Ron Hopper, who runs the FBI’s Orlando office.

And while five people were killed, “seven others’ lives were saved due to the quick actions of the officers who arrived on the scene today,” said Special Agent Danny Banks of the Florida Department of Law Enforcement.

Authorities had no reports of any specific threats the gunman made to people at the company or anyone else, Banks said.

The attack shows why people need to alert authorities whenever they learn of anything that could lead to violence, Banks said.

“If people see something that seems abnormal, they need to say something,” Orange County Mayor Teresa Jacobs added.

Sen. Bill Nelson called for more action to address mental health issues. He noted that next Monday will mark a year since the worst mass shooting in modern U.S. history, at a gay nightclub in Orlando. The attack at the Pulse club killed 49 people and wounded dozens more.

“The city of Orlando, which is still healing from the Pulse massacre, has seen too much violence this past year,” the Florida Democrat said in a statement.

Republican Gov. Rick Scott asked “all Floridians to pray for the families impacted by this senseless act of violence.”

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Associated Press Writer Freida Frisaro in Miami contributed to this report.