A mentally ill gunman who killed a hospital worker and wounded two others was upset with a doctor he thought had implanted a monitoring device during an appendectomy in 2001, police said Tuesday.

Knoxville Police Chief Sterling Owen IV said gunman Abdo Ibssa (AB'-doh IHB'-sah) first entered a medical tower near Parkwest Medical Center and asked for the doctor who performed the appendectomy. After being told the doctor wasn't there, Ibssa went to another area where patients are discharged and opened fire with a revolver.

He killed himself after shooting the three women who work at the hospital on Monday, a day before his 39th birthday.

"There was less than 5 seconds from the time of the first shot until the last shot," Owen said at a news conference.

Investigators found a note at Ibssa's Knoxville apartment in which the gunman said the doctor had implanted a chip that was being used to track his movements, Owen said.

Haloperidol, an antipsychotic medication used to treat schizophrenia and Tourette syndrome, was also found at his apartment, but investigators believe he hadn't been using it, Owen said.

Owen said relatives of the naturalized citizen from Ethiopia had him committed for mental treatment in February.

Also found during the search were a second handgun, a bag of marijuana and a copy of the book "The Official CIA Manual of Trickery and Deception" _ a reproduction of a Cold War-era CIA handbook on the use of illusion and deception for acts of espionage.

The gun used in the shooting had been reported stolen in March, while other one had an altered serial number but wasn't reported stolen. Police were not sure how Ibssa obtained either gun and said he did not have a handgun permit.

Police said Ibssa operated a convenience store near downtown Knoxville, which was closed Tuesday.

On Monday, a cab driver picked Ibssa up outside his apartment building, and the gunman told him to take him to the western side of Knoxville, eventually specifying the medical center.

Cab driver Freddys Sakhleh said Ibssa said seemed angry and depressed and said little about himself.

Ibssa directed the cab driver to the medical center tower and told to wait for him to come back. Inside, the gunman was told the doctor he sought wasn't there.

When Ibssa returned, Sakhleh said, he told the driver to take him to the hospital entrance where some patients are discharged.

Owen, the police chief, said Ibssa fired four shots at people exiting the building, hitting the three hospital workers. The gunman killed himself with a fifth shot. Police said it doesn't appear he knew the women.

"I called 911, and I said, 'Please send some people here, this man is shooting like crazy,'" Sakhleh said.

The two women who survived the shooting were taken to the trauma center at the University of Tennessee Medical Center. Owen said Tuesday afternoon the women were in stable condition.

The women's families issued statements expressing thanks for prayers and support.

The family of Ariane Reagan Guerin, a 26-year-old employee at Parkwest, said they were hearing promising information about her prognosis. The family of Nancy Chancellor, 32, said she was doing well.

The woman killed was Rachel Wattenbarger, 40. Her father, Ray Wattenbarger, said she had worked at the hospital for about five or six years, helping discharge the elderly. He said he would remember his daughter's smile.

Linda Cody, whose father was a patient at the hospital, had gone to smoke a cigarette when she saw the gunman's body, surrounded by blood. She quickly learned the victims had been shot in the same area where she normally smoked.

"It was scary," she said. "It kind of gives you the willies thinking that could have been me five seconds ago."

Sakhleh, the cab driver, said he was lucky to be alive.

"My wife always tells me, 'Be careful, be careful.' But after tonight, I'm going to be real careful."

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Associated Press writer Sheila Burke in Nashville contributed to this story.