Gunman, 3 others killed in Chicago tower

"He was not employed there, but we feel he did have previous encounters with the individuals in that office," Cline said.

Neither the victims, all men, nor the gunman were identified. A fourth victim, a woman, was taken to the hospital with a gunshot wound to the foot, but was released Friday night, said Kim Waterman, a Rush University Medical Centre spokeswoman.

Wood Phillips specializes in patent and intellectual property law, according to its Web site.

A partner at the firm, Stephen D Geimer, declined comment when reached at home by telephone Friday night.

Fire officials said they received reports of shots fired on the 38th floor around 3:15 p.m. There were about 30 people on the floor, they said.

The shooter "grabbed a hostage and he was pointing a gun alternately at the hostage's head and his own head," Cline said.

Cindy Penzick, secretary in a law firm on the 37th floor, said that after a co-worker told her she heard gunshots, a police officer with his gun drawn on their floor yelled at them to get out.

Penzick said she is usually calm, "but I have to tell you this was scary as hell."

People hurried down the escalators and ran from the skyscraper on the west side of downtown.

Keegan Greene, who works at Verizon Wireless on the first floor, was helping a customer when fire alarms began going off.

"One of the security guards came up to us and started saying, "Run, run, run, run, run!" Greene said.

Service on the Metra commuter line was suspended for more than an hour and area buses were diverted while the incident unfolded. Metra spokeswoman Judy Pardonnet said all Metra crew members had been locked into secure areas before train service resumed just after 5 p.m.