Police are still searching for a gunman after three people were shot - one fatally - during a dispute at an office complex in Phoenix, Arizona.
The suspect has been named as 70-year-old Arthur D Harmon.
Police reportedly served a search warrant on Harmon's house seven miles from the office park, but found nobody inside.
The shooting victims were taken to hospital after the incident on Wednesday morning where one man, 48-year-old Steve Singer, later died.
The other two victims, a 43-year-old man and a 32-year-old woman, remain in critical condition.
Fire Captain Scott McDonald said all the victims had sustained life-threatening wounds.
Officer James Holmes said police believe there is only one suspect, but witnesses gave conflicting information about how he left the scene.
The shooting did not appear to be a random act, said Sergeant Tommy Thompson.
He said a dispute with someone at the building became heated, and the suspect pulled out a gun and started shooting. He said he did not know what type of gun had been used.
The shooting happened as the Senate Judiciary Committee held a hearing on gun control issues, and former astronaut Mark Kelly broke news of the shooting during his testimony.
Mr Kelly is the husband of former Congresswoman Gabrielle Giffords, who was shot in the head two years ago. Ms Giffords also testified on Wednesday, appealing to her former colleagues for stricter gun laws.
The office building, in central Phoenix, was evacuated as police searched for the suspect and any additional victims.
Vanessa Brogan, who works in an insurance office in the three-storey complex, said she heard a loud bang that she first thought had been made by someone working in or near the building.
She said other people thought they heard multiple loud noises. She said people locked themselves in offices until police evacuated the business park.
The complex houses insurance, medical and law offices.
Becky Neher, who also works in the building, said she heard two gunshots and saw two victims lying on the ground outside the back of the building.
"Someone yelled 'We have a shooter', " she said.
Ms Neher said medical workers who have offices in the complex came out to help the victims.