(CNN) -- The gunman in Monday's fatal shooting spree at an Orlando, Florida, business targeted his victims and had a "negative relationship" with at least one of them, Orlando County Sheriff Jerry Demings said.
"He was certainly singling out the individuals he shot," Demings told reporters Monday afternoon.
Police say he killed five employees of Fiamma Inc. before killing himself.
The gunman was identified as John Robert Neumann, Jr.
He was fired in April by Fiamma Inc., which makes accessories for recreational vehicles.
Monday morning, he pointed his gun at a new, temporary employee and told her to leave, Demings said.
Police identify victims
Demings named the victims as Robert Snyder, 69; Brenda Motanez-Crespo, 44; Kevin Clark, 53; Kevin Lawson, 46; and Jeffrey Roberts, 57.
Neumann lived alone and had no family in the area, Demings said. He was an Army veteran who was honorably discharged in 1999.
Police said Neumann was a disgruntled former employee acting alone and had no ties to terror or subversive groups.
Demings said it did not appear Neumann had a concealed weapons permit for the semi-automatic pistol he used.
Police responded to the call about 8 a.m. in an industrial area northeast of downtown.
Three men and a woman were found dead at the scene, Demings said. Another man died at Orlando Regional Medical Center.
"Most of the victims were shot in the head," Demings said. "Some were shot multiple times."
Eight other people were inside the business when the shootings took place, he said.
'My boss is dead'
Shelley Adams told reporters she spoke Monday with her sister, who works at Fiamma and was in the restroom when she heard a noise.
Her sister came out and saw someone lying on the floor.
"She said, 'I saw too much. My boss is dead,'" Adams said.
Shooter was fired this year
Police had responded to a battery complaint against Neumann at Fiamma in 2014. The victim of that incident was not among the dead Monday, Demings said.
Neumann had a minor police record including arrests for DUI and marijuana possession.
Pulse anniversary approaches
Almost a year ago, Orlando was the site of the nation's worst terror attack since 9/11. On June 12, 2016, a gunman killed 49 people at the Pulse nightclub.
"Over the past year, the Orlando community has been challenged like never before," Florida Gov. Rick Scott said in a statement Monday.
"I will remain in contact with the Orlando law enforcement community throughout the day as more information is made available," Scott said.
CNN's Tina Burnside and John Couwels contributed to this report.
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