Jason Rodriguez, 40, surrendered about three hours later, after officers saw him through the window of his mother's home and asked him to come outside, Orlando Police Chief Val Demings said.
Asked by a reporter outside the police station why he did it, he replied: "Because they left me to rot."
Demings said Rodriguez brought a handgun to the firm in a downtown office tower where he once worked as an engineer, but investigators are not sure what his motive was.
"This is a tragedy, no doubt about it, especially on the heels of the tragedy in Fort Hood that is on our minds," Demings said. "I'm just glad we don't have any more fatalities or any more injuries than we currently have."
Charles W. Price, an attorney who represented Rodriguez in a bankruptcy case, declined to comment.
Camille Previlon told The Associated Press her uncle, engineer Guy Lungenbel, was shot in the back and was able to talk but had not said much about the shooting.
"He is stable," she said. "He's just hurting real bad in the back."
Everyone who was shot was in the offices of Reynolds Smith & Hills, on the eighth floor. The five survivors were in stable condition, Demings said.
A somber Gov. Charlie Crist visited some of the wounded at Orlando Regional Medical Center on Friday afternoon.
"They're obviously traumatized," he said. "At the same time, I was impressed with their spirit and strength."
He said he was thankful the shooting was not worse and said the victims "felt very lucky and blessed to be alive."
Reynolds Smith & Hills spokesman Mike Bernos said Rodriguez was an entry-level engineer who was fired in June 2007 after working there for a year.
"His performance wasn't up to our standards, so we terminated him," Bernos said. There had been no contact between the company and Rodriguez since then.
After the lunchtime shooting, some people streamed out of the Legion Place building while others holed up in their offices. A major highway was closed and nearby schools were locked down.
Greg Cross, who works in a real estate office on the 12th floor, said he and his co-workers barricaded themselves inside after hearing about the gunman on television.
"We were terrified," he said. "We locked the door and put a filing cabinet in front of the door and just waited."
Mark Vella, who works in a different office on the same floor, said he and five co-workers also pulled a filing cabinet in front of their door. They prayed and talked about what to do if the gunman showed up.
"It was a little scary, a little unnerving," Vella said. "We were afraid the guy was still in the building and making the rounds."
Associated Press writers Travis Reed, Kelli Kennedy, Jennifer Kay, Laura Wides-Munoz, David Fischer and Damian Grass in Miami; Antonio Gonzalez, Mitch Stacy and Tamara Lush in Orlando; and Christine Armario in Tampa contributed to this report.