The gunman who fatally shot three people in a law firm's high-rise office before he was killed by police felt cheated over an invention, authorities said Saturday.
Joe Jackson forced a security guard at gunpoint to take him up to the 38th-floor offices of Wood, Phillips, Katz, Clark & Mortimer, which specialized in intellectual property and patents. He carried the revolver, a knife and hammer in a large manila envelope and chained the office doors behind him, police said.
Jackson, 59, told witnesses before he was shot that he had been cheated over a toilet he had invented for use in trucks, police Superintendent Phil Cline said Saturday.
He was holding a hostage at gunpoint Friday when SWAT officers shot him from about 45 yards away, Cline said.
"He had already shot four people. He had reloaded his gun," Cline said Saturday. There were 25 to 30 other people on the floor at the time, Cline said earlier.
The Cook County Medical Examiner's Office identified the victims Saturday as Michael R. McKenna, 58, of Chicago; Allen J. Hoover, 65, of Wilmette; and Paul Goodson, 78, of Chicago.
Colleagues told reporters Hoover was a partner at the firm and McKenna was a patent attorney who rented space. They said Goodson worked part time, sorting mail and making deliveries.
Jackson had McKenna's business card in his pocket, Cline said.
"We know he went there for Mr. McKenna, then he continued to shoot other people," Cline said Saturday.
Cline said Jackson had tried at least one other time Friday to go up to the firm's offices but was turned away.
In 1968, Jackson was arrested for unlawful possession of a weapon and in 1977 for a stolen motor vehicle and disorderly conduct.
Police said McKenna's longtime paralegal, Ruth Zak Leib, 57, was treated for a gunshot wound to the foot and released Friday, Rush University Medical Center said.