PHOENIX -- A man who shot and killed a call-centre CEO and critically wounded a lawyer at a Phoenix office building where they were meeting to discuss a contract dispute was found dead early Thursday, ending a nearly 24-hour manhunt that had area residents on edge.

A landscaper found the body of Arthur Douglas Harmon among some bushes in the Phoenix suburb of Mesa. Harmon, 70, died of an apparent self-inflicted gunshot wound, police said.

A handgun was found near his body, and a rented Kia Optima sedan that he drove from Wednesday's shooting scene was located in a nearby parking lot.

Authorities had been searching for Harmon since Wednesday morning, when they say he drew a gun and shot two men at the end of a mediation session at a north-central Phoenix office building.

Steve Singer, 48, died hours later. The law firm that employs Mark Hummels, 43, said Thursday he is on life support and isn't expected to survive.

A third person, 32-year-old Nichole Hampton, was caught in the gunfire near the office building's entrance and suffered a gunshot wound to her left hand. The mother of two is recovering and expects to be discharged from a hospital Friday.

Hampton works for another company inside the office complex and wasn't involved in the contract dispute. She told reporters Thursday that she never saw Harmon or the two men who were shot.

"We believe the two men were the targets," Phoenix police Sgt. Tommy Thompson said. "It was not a random shooting."

Harmon also fired at someone who tried to follow him to get his license plate number, authorities said.

Singer was the CEO of Fusion Contact Centers LLC, which had hired Harmon to refurbish office cubicles at two call centres in California.

According to court documents, Harmon was scheduled to go to a law office in the building where the shooting took place for a settlement conference in a lawsuit he filed against Fusion in April.

Harmon represented himself in the lawsuit, and Hummels represented Fusion.

Colleagues of Hummels described him as a smart, competent and decent man who was a rising star in his profession and dedicated to his wife, 9-year-old daughter and 7-year-old son.

"This is a day of just unspeakable sorrow," said 9th U.S. Circuit Court of Appeals Judge Andrew Hurwitz, who hired Hummels straight out of law school to serve as a law clerk from 2004 to 2005 while Hurwitz was serving on the Arizona Supreme Court.

The response to the shooting first centred on that building -- home to insurance, medical and law offices -- but soon spread to a north-Phoenix home and a central-Phoenix high-rise where Hummels' office is located.

SWAT teams and two armoured vehicles surrounded the house. Police served a search warrant to enter the home, which county property records show was sold by Harmon to his son last year for $26,000.

For a time, officers used a megaphone to ask Harmon to surrender, believing he might be inside the residence.

Harmon's body eventually was found near a shopping area about 14 miles (22 kilometres) from the office building where Wednesday's shooting occurred. Police didn't immediately know how long it had been there.

The shooting took place on the same day that hearings on legislation to address gun violence were convened in Washington, with former Arizona Rep. Gabrielle Giffords testifying for stricter gun controls. A gunman shot Giffords in the head during a shooting rampage in Tucson in January 2011.