A mentally ill gunman who killed a US hospital worker and wounded two others was upset with a doctor he thought had implanted a monitoring device during an appendectomy in 2001, police have said.
Knoxville Police Chief Sterling Owen IV said gunman Abdo Ibssa first entered a medical building near Parkwest Medical Centre and asked for the doctor who performed the appendectomy.
He then went to another area where patients are discharged and opened fire. He killed himself after shooting three women on Monday, a day before his 39th birthday.
"There was less than five seconds from the time of the first shot until the last shot," Owen said at a news conference.
Owen said investigators found a note at Ibssa's apartment in which the gunman said the doctor had implanted a chip that was being used to track the patient's movements.
Medication used for treating a psychological condition was also found at his apartment, but investigators believe he had not been taking his medicine, Owen said. Owen said relatives of the naturalised citizen from Ethiopia had him committed for mental treatment in February.
A copy of the book "The Official CIA Manual of Trickery and Deception" was also at his apartment.
Cab driver Freddys Sakhleh has said he picked up the gunman outside an apartment complex, and the man told him he wanted to go to the western side of Knoxville.
They stopped at an ATM, where the suspect withdrew 20 dollars before telling Sakhleh to take him to the medical centre complex. Sakhleh said the man seemed angry and depressed and said little about himself, only that he was from Atlanta.
Sakhleh said the man then got out of the cab, handed him 20 dollars and told him to wait five minutes. He returned, grabbed a gun from his waist and started shooting. "All of this happened in a matter of seconds," the driver said, adding that he called police dispatchers to report the incident.