The man suspected of killing six people and seriously wounding a US congresswoman in the state of Arizona has been charged with murder and attempted murder a day after a shooting rampage.
Prosecutors filed five separate charges against Jared Loughner, 22, in the federal court in Phoenix on Sunday over the attack.
The US justice department said Loughner, who is due to appear in court on Monday, is suspected of shooting more than a dozen people including Gabrielle Giffords, a US congresswoman, at a political event hosted by her in Tucson.
John Roll, a US federal judge, and Gabriel Zimmerman, one of Gifford's aides were among the six people killed in Saturday's incident.
Giffords, 40, who represents Arizona's eighth congressional district in the House, is said to be responding well to treatment after being shot in the head.
The Democrat was "able to communicate" by following simple commands, but had not yet spoken, one of her trauma surgeons said on Sunday.
Noting that the bullet did not cross through the centre of Giffords' brain, Michael Lemole, chief of neurosurgery at University Medical Centre, said: "[She] is able to communicate with us this morning through following simple commands.
"We're very encouraged by that. We are still in critical condition. Brain swelling at any time can take a turn for the worse. But I am cautiously optimistic."
Daniel Hernandez, one of Giffords' interns who was present at the time of the shooting, went to her aid after she was shot.
"When I heard the gunshots, my first instinct was to see how the congresswoman was doing, because I knew if there was a gunman the likely target would probably be the congresswoman," he told Al Jazeera.
"I noticed the congresswoman had been shot in the head, and I made her my first priority.
"I applied pressure to make sure the congresswoman did not bleed out. So I had someone else grab clean linens, which I used. But until that point I was using my bare hands to apply pressure to make sure the congresswoman did not bleed out."
Message from suspect
Earlier, investigators said they carried out a search at the suspect's home and seized an envelope from a safe with messages such as "I planned ahead", "My assassination" and the name "Giffords" next to what appears to be the man's signature.
Saturday's shooting has shocked politicians in Washington, where congress postponed a vote on healthcare reform later this week.
Arizona authorities say a second man has been cleared of any involvement in the attack.
Jason Ogan, Pima County sheriff's deputy, said the man "came by, and we talked to him and we determined he was not involved".
He also said authorities were not ready to say if they are confident the armed man acted alone.
Following an acrimonious campaign in the run-up to last November's midterm congressional elections, some commentators were quick to cite a shrill climate of political vitriol might have played a role in the shooting.
| Giffords, who is married to Mark Kelly, a NASA astronaut, represents Arizona's eight district [AFP]
"We are in a dark place in this country right now and the atmospheric condition is toxic," Democratic representative Emanuel Cleaver told NBC's Meet the Press.
The suspected attacker opened fire with a semi-automatic pistol at point-blank range outside a supermarket.
Six people, including a US federal judge and a nine-year-old girl, were killed in the attack, with Giffords and 13 others wounded.
Police seeking a motive for the shooting spree were looking at a trail of anti-government messages on the internet left either by Loughner or someone writing under that name.
There was no coherent theme to the messages.
John Boehner, the US House of Representatives speaker, ordered flags at the US Capitol in Washington lowered to half staff in memory of the victims.
Boehner said the incident was a reminder that public service comes with a risk.
"This inhuman act should not and will not deter us from our calling to represent our constituents and fulfil our oaths of office. No act, no matter how heinous, must be allowed to stop us from our duty," Boehner said.
In Tucson, Clarence Dupnik, the Pima County sheriff, said the suspect "has kind of a troubled past and we're not convinced that he acted alone".
He said he believed Giffords was the intended target of the shooting.
Dupnik said the suspect had made threats to kill in the past but not against Giffords.
Barack Obama, the US president, has put Robert Mueller, the FBI director, in charge of the investigation, with a team heading to the scene of the murders.