The remaining two victims' injuries were not life-threatening, Sgt. Tommy Thompson said.
Police do not believe the shooting was a random act, Thompson said. Authorities said police so far believe there was only one shooter but don't know where he is.
The gunfire prompted terrified workers throughout the complex to lock the doors to their offices and hide far from the windows. SWAT officers searched the building.
“Everyone was just scared, honestly, just scared,” said Navika Sood, assistant director of nursing at First at Home Health Services who along with her co-workers locked the entrances to their office.
Sood said authorities evacuated the office about 30 minutes after she first heard the popping noises.
The shooting took place on the same day that hearings on legislation to address gun violence were convened in Washington, with former Rep. Gabrielle Giffords testifying for stricter gun controls.
A gunman shot Giffords in the head during a shooting rampage in Tucson in January 2011.
Around 10:30 a.m., the gunman arrived at the office building and got into a dispute with someone, a conflict that escalated to the point where he drew a gun and shot three people, Thompson said.
Vannessa Brogan, who works in sales support at an insurance business in the three-story complex, said she heard a loud bang that she thought at first was from somebody working in or near the building.