US Congresswoman Gabrielle Giffords is battling for her life today after an attacker shot her in the head and killed six others as she met constituents in Tucson, Arizona.
The 40-year-old Democrat, who is married to a Nasa astronaut, is in a critical condition in hospital but doctors are optimistic she will survive.
The suspected gunman is in custody as investigators seek a motive for the shooting and search for a possible accomplice.
Ms Giffords was hosting a "Congress on Your Corner" event - public gatherings to give her constituents a chance to talk directly with her - outside a supermarket when the gunman attacked.
He approached Ms Giffords from behind and opened fire with a semi-automatic pistol at point-blank range, reportedly firing at least 20 shots at her and others in the crowd.
The suspect, identified as Jared Lee Loughner (22), was tackled by two bystanders after the shooting.
CNN has named the people who died at the scene as Chief Judge John Roll (63) of the US District Court for Arizona; Giffords staff member Gabe Zimmerman (30); Dorwin Stoddard (76), who died shielding his wife from the bullets; Dorothy Morris (76) and 79-year-old Phyllis Scheck.
Christina Taylor Green (9), was pronounced dead in hospital. She was born on September 11th, 2001, according to local media. Her uncle told the Arizona Republic that a neighbour was going to the event and invited her along because she had just been elected to the student council and was interested in government.
Twelve other people were wounded.
The shooting shocked Washington, where Congress postponed a vote on healthcare reform later this week. Following an acrimonious election campaign last year, some suggested the political vitriol might have played a role in the shooting.
Pima County Sheriff Clarence Dupnik said the suspect "has kind of a troubled past and we're not convinced that he acted alone." He said he believed Ms Giffords was the intended target of the shooting.
Sherriff Dupnik said the suspect had made threats to kill in the past but not against Ms Giffords. "All I can tell you is that this person may have a mental issue," he added.
The sheriff's office said today authorities they were still seeking a second man "possibly associated with the suspect" who was filmed by a video camera near the scene and is wanted for questioning. He is described as a white man in his early 40s with dark hair.
President Barack Obama put FBI director Robert Mueller in charge of the investigation. "We don't yet know what provoked this unspeakable act," Mr Obama told reporters.
Ms Giffords was shot once in the head with the bullet going "through and through," according to a trauma surgeon at the Tucson hospital where she was airlifted for surgery.
She is able to communicate and follow simple commands, a neurosurgeon at the hospital said today. "We are very encouraged by that," Dr Michael Lemole Jr said. "I am cautiously optimistic."
Hospital spokeswoman Darcy Slaten said five people were in critical condition today and five in serious condition. She said the three other wounded were treated and released.
Mark Kimball, a communications aide for Ms Giffords, described the scene as “just complete chaos, people screaming, crying”. He said the gunman fired at Ms Giffords and her district director and started shooting indiscriminately at staffers and others standing in line to talk to the congresswoman.
“He was not more than three or four feet from the congresswoman and the district director,” he said.
The shooting prompted the postponement of the Capitol agenda for next week, including a vote on the repeal of Mr Obama's contentious healthcare overhaul. The new Congress convened last week after elections in November in which the Republican Party won control of the House of Representatives.
House Speaker John Boehner said in statement he was horrified by the attack on Ms Giffords and members of her staff.
Ms Giffords had warned previously that the heated political rhetoric had prompted violent threats against her and vandalism at her office.
In an interview last year with the MSNBC television network, she cited a map of electoral targets put out by former Alaska Republican governor Sarah Palin, each marked by the crosshairs of a rifle sight. "When people do that, they've got to realise that there's consequences to that action," Ms Giffords said.
In several videos posted on YouTube, a person who posted under the name Jared Lee Loughner criticises the government and religion and calls for a new currency.
"The government is implying mind control and brainwash on the people by controlling grammar. No! I won't pay debt with a currency that's not backed by gold and silver! No! I won't trust in God!" The FBI is investigating whether the shooting suspect was the same person who posted the videos.
In a biographical sketch on the site, the author of the post writes that he attended Tucson-area schools and that his favourite books include Adolf Hitler's Mein Kampf, Karl Marx's Communist Manifesto, and Ken Kesey's One Flew Over the Cuckoo's Nest.
Ms Giffords is seen as a rising star in the Democratic Party. She narrowly defeated a conservative opponent and was one of the few Democrats to survive the Republican sweep in swing districts in the November elections. Her state has been at the centre of a political firestorm the past year, symbolising a bitter partisan divide across much of America.
The spark was the border state's move to crack down on illegal immigration last summer, a bill proposed by conservative lawmakers and signed by Republican Governor Jan Brewer.
Most Arizonans supported it, but opponents and many in the large Hispanic population felt it was unconstitutional and would lead to discrimination. Ms Giffords said it would not secure the border or stop drug smuggling and gun running.
The US Capitol Police cautioned members of Congress "to take reasonable and prudent precautions regarding their personal security. Most are largely unguarded outside the Capitol, except the leaders of the House and Senate, who have security details.
Agencies