ORLANDO, Fla. — 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 belong to any type of subversive or terrorist organization.

The shooting began after Neumann slipped through a rear door into the cavernous Fiamma Inc. 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.

State and federal law enforcement officers converged on the 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.

That woman had been hired after Neumann was fired in April, so he probably did not recognize her and knew she was not a former co-worker, Deming said.

Searching for a motive, deputies cordoned off a trailer park in Maitland, where Neumann lived alone in a mobile home on a busy road next to a funeral home, a used car lot and a dog-grooming business. Like the awning factory, it’s far from Orlando’s famous theme parks.

Deming said investigators also are 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 was not 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 factory, when he was accused of battering a co-worker in June 2014. But no charges were filed after both men were interviewed, and that co-worker was not among Monday’s victims, the sheriff said.