PHOENIX — A gunman opened fire at an office complex here on Wednesday, killing one man and injuring two others before speeding away, the police said. Three other people were hospitalized for stress brought on by the shooting.

A police spokesman identified the gunman as Arthur Harmon, 70.

The gunman opened fire just outside the lobby of the office complex after a mediation session at a law firm in the building over a lawsuit he had filed against a call center based in Scottsdale, Ariz., the authorities said. The call center’s chief executive, Steven Singer, 48, who was at the session, was killed.

The shooting took place around 10:30 a.m. in the lobby of a three-story commercial building on North 16th Street, in the heart of the city. The police spokesman, Sgt. Tommy Thompson, said it was “not random.” The gunman “came here for a reason,” he said from the scene.