Sgt. Tommy Thompson said police do not believe the shooting about 10:30 a.m. was a random act. He said one person was in extremely critical condition. Two others who were shot had less severe injuries, but all the injuries could be life-threatening, said Fire Capt. Scott McDonald.
Officer James Holmes said police so far believe there was only one shooter but don't know his whereabouts.
"We have no motive. It is right now a really fluid scene," Holmes said.
He said police were given conflicting information about the suspect leaving the scene. The building was evacuated and police are looking for a suspect or any additional victims.
Navika Sood, assistant director of nursing at First at Home Health Services, said she heard a handful of loud popping noises Wednesday morning. She said she and her co-workers locked the entrances to their office and gathered in one area away from the windows.
"Everyone was just scared, honestly, just scared," she said.
Sood said authorities evacuated the office about 30 minutes after she first heard the popping noises.
Vannessa Brogan, who works in sales support in 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. She said others at the business thought they heard multiple loud noises. She said people locked themselves in offices until authorities evacuated the central Phoenix building that houses insurance, medical and law offices.
Becky Neher, who works for a title company in the building said the two gunshots she heard sounded like two pieces of metal banging against each other.
"We were doing our regular morning routine, and I hear what I guess were two gunshots," she said.
Watching from her second-story office, she saw people leaving the building, she was watching from her second story office.
"Someone yelled, 'We have a shooter,'" she said. She saw two victims lying on the ground outside the back side of the building. She said there are medical people who have offices in the complex, so they came out to help.