Phoenix Police Department Phoenix police were seeking Arthur Douglas Harmon, 70, in the deadly shooting at a Phoenix business comples Wednesday, Jan. 30.

A man shot three people, killing one of them, after a dispute at a Phoenix office complex Wednesday, authorities said.

Phoenix police said that the gunman fled the scene. The suspect was identified as Arthur Harmon, 70, of Phoenix. He was described as a white male, about 6 feet tall and about 220 pounds, and was considered armed and dangerous.

Steven Singer, 48, was pronounced dead at a Phoenix hospital, police said. Authorities wouldn't discuss the identities or conditions of the two other victims, a white man and a woman in her early 30s, because Harmon was still at large.

Three other people were also treated for "stress-related" conditions after the incident at a business complex near 16th Street and Glendale Avenue, authorities said.

A police SWAT unit that arrived at Harmon's home in a residential neighborhood about five miles away discovered that he wasn't there. Later Wednesday afternoon, more police swarmed outside a downtown Phoenix office tower where a vehicle may have been found that was similar to the one witnesses said the gunman drove off in. Yellow crime scene tape was put up in the tower's plaza.

Phoenix police Sgt. Tommy Thompson said the incident was believed to have begun with an altercation in the lobby of the complex that escalated into gunfire.

"The initial indications are that this was not a random act," he said.

Police said shell casings at the scene indicated that at least two weapons were used.

Prominent lawyer wounded

Mark P. Hummels, president of the Phoenix chapter of the Federal Bar Association, was among the shooting victims, his law firm said in a statement. It said Hummels was representing a client in a mediation session when he was shot.

Mark Kelly, husband of former Rep. Gabrielle Giffords, who was critically wounded by gunfire in 2011, interrupts his testimony before a Senate hearing on gun control to share news of the workplace shooting in Phoenix.

Hummels was being treated at John C. Lincoln Hospital, the firm said, adding that it had no information on his condition.

Jim Fink, a neighbor of Harmon's for many years, told The Arizona Republic that Harmon had recently been involved in a business lawsuit and had been "confident that he was going to win this case."

"He was a great neighbor," Fink said. "Wouldn't trade him for the world."

Witnesses to the shooting said they heard nine or 10 shots. A woman who works in the building told NBC station KPNX of Phoenix that she immediately began running down the hallway.

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"We didn't know where to hide, because all of our offices are all windows," she said.

The shootings occurred during a Senate hearing on gun violence where former Rep. Gabrielle Giffords, D-Ariz., made a brief statement urging new gun control measures. Giffords was critically wounded in a mass shooting in Tucson, Ariz., in 2011.

Giffords' husband, Mark Kelly, broke the news of Wednesday's shooting to members of the Senate Judiciary Committee, interrupting his own answer to a question from Sen. Richard Blumenthal, D-Conn.

"While we were having this hearing, ... in Phoenix, Arizona, there is another what seems to be, possibly, a shooting with multiple victims," he said.

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