Congresswoman Gabrielle Giffords, who officials believe was the target of the shootout remained in critical condition after the brain surgery, though doctors said they were hopeful of her recovery.
The bullet, from a semiautomatic pistol, entered her head from the front and exited through the rear after passing through her brain in what doctors described as a "through and through" injury.
The mass shooting that besides gravely wounding Giffords, killed a federal judge amongst five more people, has shocked the nation and raised concerns that the heated political discourse had taken a dangerous turn.
Giffords underwent brain surgery after the shooting that authorities said was a targeted attempt on her life.Neurosurgeons at University Medical Center in Tucson operated on the Congresswomen, and doctors were hopeful she would recover, Dr Peter Rhee said during a news conference at the hospital.
Giffords was following commands, which is a good sign, he said.C J Karamargin, Giffords' communications director said that Giffords remained in critical condition in intensive care and was not fully conscience.
However, he said Gifford's deputy director Ron Barber, who was wounded in the shooting, was "doing very well" and speaking."I'm very optimistic about her recovery," Rhee said.
Six people were killed and 13 others were injured in the volley of bullets.The 40-year-old Arizona Democrat was meeting constituents for the first time since surviving a bruising re-election campaign last fall.
The Democrat had drawn the ire of critics on the hot- button issues of immigration and the health-care reform. In fact, a vandal had shattered a window of her Tucson office in the days after she cast a vote in favour of the president's health care bill.It was the first time in more than 30 years that a US lawmaker was the victim of an assassination attempt.
Police are holding a 22-year-old man in the shooting rampage, which occurred outside a supermarket where Giffords was greeting constituents.The gunman shot Giffords in the head at close range and then continued to fire into the small gathering of people.
Law enforcement and medical officials in Arizona said that at least 18 people were shot in the melee and that six of them had died, including John M Roll, the chief US District judge in Arizona, and Gabe Zimmerman, Giffords's local director of community outreach.
Also killed was Christina Taylor Green, a nine-year- old girl, who was born on Sept 11, 2001, and had gone to the event with a neighbour.
Two other Giffords' staffers, district director Barber and community outreach aide Pam Simon, were wounded.
Authorities said they were seeking a second man as a "person of interest" who might have been at the scene with the gunman.He is not a suspect in the shooting, authorities said.Police said the suspect, whom they would not identify, has refused to cooperate with authorities, invoking his right to remain silent.
Police believe he came to the constituent meeting with another individual identified only as a white male in his 50s.
Multiple law-enforcement sources say police were questioning Jared Loughner, a 22-year-old Tucson man whose online writings and videos are filled with anti-government messages and rambling rants about mind-control and brainwashing.
Authorities also confirmed that a suspicious package was left at Giffords' Tucson headquarters sometime yesterday and was being investigated.Emotions burst to the surface as news of the shooting spread.
President Barack Obama promised the full resources of the federal government for what he called an unspeakable act.
The president dispatched FBI Director Robert Mueller to oversee the federal investigation.
Gov Jan Brewer, fighting tears, said she was heartbroken by the tragic events and called Giffords a friend she had come to love and respect.
Pima County Sheriff Clarence Dupnik was visibly angry as he briefed reporters in Tucson, repeating his belief that the gunman may have been motivated in part by hate-infused talk on radio and television.
"I think it's time as a country to do a little soul-searching," Dupnik said.
"The anger, the hatred, the bigotry that goes on in this country is getting to be outrageous".
The shooting is almost certain to ratchet up the political debate on issues of immigration and health-care reform which have gereated bitter political debate in the past year.
Immigration helped drive an often bitter election campaign against her Republican opponent Jesse Kelly