At least three people were shot on Wednesday at a business complex in Phoenix, and one was in an extremely critical condition, police said.
Phoenix Police Department Sergeant Tommy Thompson said, "initial indications are that this is not a random act." The building is in a mixed-used office block at a busy intersection.
He said a suspect had gone to the building at about 10:30 am, argued with someone inside, and opened fire.
Two other people were taken to hospital for "stress related symptoms," he said.
The shooting comes at a time of heightened fear in the United States over gun violence since a gunman shot and killed 20 children and six adults at a Connecticut school in December.
Frank Kirby, a financial planner who works in a nearby office, said he was outside his building immediately after the incident.
"We hear a gunshot and then immediately we hear a car come roaring down that street. We look up and it's coming backward down that road," Kirby said in a phone interview.
"He actually comes backwards, northbound on 16th street," he said. "He gets beyond my building just about even, spins around and takes off now going the proper direction."
Kirby said he did not witness the shooting at the office but saw two people being carried from the building on stretchers.
Ambulances and dozens of police vehicles were at the office complex. Police said they were searching for a white man in his sixties with gray hair.
"Some say he left the building in a vehicle, and some say that he was still inside, so that's kind of where we are at," police spokesman Holmes said.
Police evacuated the offices in central Phoenix.