ORLANDO — John Robert Neumann Jr., was fired in April from his job at a factory here that manufactures awnings and accessories for recreational vehicles. He returned to the isolated industrial area on Monday morning, authorities said, armed with a semiautomatic handgun and a hunting knife.

Neumann crept in through a rear door at Fiamma, authorities said, apparently looking for specific company employees. He at one point encountered a woman, pointed a gun at her and told her to get out of the building, and the woman told investigators that she was allowed to leave unharmed. Then he allegedly singled out other employees, shooting and killing five former colleagues. He stopped at least once to reload.

“Most of the victims were shot in the head,” Orange County Sheriff Jerry L. Demings said during an afternoon news conference. “Some were shot multiple times.”

When deputies arrived at the scene, they found four people dead — three men and a woman. A fifth was rushed to a hospital, where he also died, Demings said. The victims were identified by police as Kevin Clark, 53; Jeffrey Roberts, 57; Robert Snyder, 69; Brenda Montanez-Crespo, 44; and Kevin Lawson, 46. According to the Orlando Sentinel, Clark’s wife died in 2008 and he leaves behind two children, 14 and 18 years old.

Neumann, the sheriff said, appeared to have committed suicide before police arrived.

Demings said that about eight other people inside the building were not injured in the attack. Authorities said they believe the rampage was the result of Neumann’s history with the company —  Demings called Neumann a “disgruntled employee” who had a “negative relationship” with at least one of the victims.

“We have no indication that this subject is a participant in any type of terror organization,” Demings told reporters Monday morning. “What this is at this point is likely a workplace violence incident.”

The sheriff did not say why the company fired Neumann, but he noted that about three years ago, deputies responded to an incident at the business in which Neumann was accused of battering another employee. Deputies did not file charges in the incident, Demings said.

Neumann, a U.S. Army veteran who was honorably discharged in 1999, had a criminal history that included a DUI and minor drug possession, Demings said. The sheriff said Neumann did not have a concealed-weapons permit.

The shooting occurred in an industrial area about seven miles northeast of downtown Orlando, on the opposite side of the city from Disney’s Magic Kingdom. The area around Fiamma includes textile companies, body shops, kitchen equipment suppliers and other small businesses.

Following the shooting, Shelley Adams told reporters that her sister, who works at Fiamma, was in the restroom Monday when she heard a bang. When she came out, she saw someone on the floor.

Adams said her sister called and kept repeating: “My boss is dead. My boss is dead.”

Luiz Gonzalez, 61, who owns Esperanza Shoe Repair in a business strip across the street from Fiamma, said about 8 a.m. Monday that he heard someone screaming outside his shop. He said he ran to the front door and found a woman pleading with a passer-by to use a phone.

“I was surprised,” Gonzalez said. Moments later, he said, the police were everywhere. “People came running out. Police got them across the street on this side.”

The FBI dispatched members of the bureau’s Orlando office to the scene, where they are assisting in the investigation and working to determine the motivation, officials said.

Authorities did not immediately comment on a specific motive for the shooting, which occurred just a week before the anniversary of the Pulse nightclub massacre in downtown Orlando. That mass shooting left 49 people dead and injured dozens of others. The attacker at Pulse, who was killed by police after an hours-long standoff inside the club, had pledged allegiance to the Islamic State.

Florida Gov. Rick Scott (R) asked residents across the state to pray for the families affected “by this senseless act of violence.”

“Over the past year, the Orlando community has been challenged like never before,” Scott said in a statement. “I have been briefed by our law enforcement officials on this tragic incident and Ann and I are praying for the families who lost loved ones today.”

Orange County Mayor Teresa Jacobs (R) said, “Unfortunately, we’ve seen this scenario play itself out in our community and in other communities across the nation, and it is incumbent upon all of us not to become complacent or become callous to these horrific situations, but for each of our citizens to be vigilant . . . if they see something that seems abnormal, they need to say something.”

This story has been updated. Bever and Berman reported from Washington.