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A look at what is known so far about how the gun attack on Congresswoman Gabrielle Giffords and 17 others in Arizona unfolded.

A gunman opened fire just after 1000 local time (1700 GMT) on Saturday as Congresswoman Gabrielle Giffords was meeting constituents in the city of Tucson.

Ms Giffords was shot in the head at close range - witnesses said the gunman was only a couple of feet away - and 19 others also suffered gunshot wounds.

Ms Giffords was flown to a hospital in Tucson for emergency surgery, after which her surgeon said he was "optimistic" she would survive. She is still in intensive care.

Five people were killed at the scene and one died in hospital. Among the dead were federal Judge John Roll, a nine-year-old child and one of Ms Giffords's political aides.

Two other members of Ms Giffords's staff were said to be among the injured.

Police believe the congresswoman was the intended target of the attack.

The shooting occurred outside a Safeway supermarket at a shopping centre called La Toscana Village, in a north-western area of Tucson.

Ms Giffords was holding a "Congress on Your Corner" event, intended to give voters a chance to address her directly. She has done about 20 such events previously, her spokesman said.

A volunteer told the Arizona Daily Star newspaper that the gunman had approached him and asked to speak to Ms Giffords.

The man went to the back of the line, as asked, before walking towards Ms Giffords a few minutes later and opening fire, the volunteer said.

Another witness told the newspaper he heard another 15 to 20 rounds being fired after Ms Giffords fell to the floor.

As the man tried to load another magazine one woman, Patricia Maisch, tore it from him.

The gunman loaded a third magazine, but its spring failed. Two men, Roger Salzgeber and Bill Badger, then wrestled the gun away and subdued him.

The suspect was then taken into custody.

There was no security presence at the "town hall" style meeting, police said.

A Giffords' intern, Daniel Hernandez, said he applied first aid to the congresswoman, staunching the blood from her head wound before she could be taken to hospital for surgery.

The alleged gunman has been confirmed by the FBI as Jared Loughner, aged 22.

Pima County Sheriff Clarence Dupnik said the suspect had used a semi-automatic pistol to carry out the shooting.

US media reported that the gun was a Glock 19, and had been bought legally in Tucson.

Police had released a photograph of a second man they wanted to question, but Pima County Sheriff's Deputy Jason Ogan said the man had been cleared of any involvement - he was a cab driver who drove the gunman to the grocery store.

The suspected gunman in custody - thought to have attended Pima College in Tucson - may have "a mental issue", the sheriff said. He is not co-operating with investigators.

A statement from the US Army said the alleged gunman had sought to enlist but was unsuccessful.

"In accordance with the Privacy Act, we will not discuss why he was rejected," the statement said.

An old schoolmate of Mr Loughner told the Associated Press news agency he was a cannabis-smoking loner.

Police are poring over a series of rambling messages posted on the YouTube website believed to be the work of the suspect.

One message, written in white text over a black background, talks of inventing a new US currency.

Another suggests that the government practises "mind control and brainwash" by "controlling grammar".

One victim has been identified as Judge John Roll, who was appointed to the US District Court for Arizona by President George Bush Sr in 1991.

He reportedly received many death threats in 2009 when he allowed a $32m (£21m) lawsuit filed by illegal immigrants against an Arizona rancher to proceed. More than 200 threatening phone calls were made to his office on one day.

Officials at the time said many of the threats were stirred up by right-wing talk-back radio. He received police protection for a month as a result.

Authorities do not believe he was a target of Saturday's attack. Local media said he had recently worked with Ms Giffords on court issues, and was merely stopping by to see her at the constituent event when he became an unfortunate victim of the shooter.

The other victims as:

Mr Stoddard, a church volunteer, was shot in the head as he tried to protect his wife, who was injured but is expected to survive, the