Paul Wellman laid his handwritten sign among the collection of candles, flowers and messages keeping vigil outside congresswoman Gabrielle Giffords's office. Then he stepped back and surveyed the scene.

To the right, another sign said: "Hate speech = murder". But Wellman went further with his angry declaration in large black letters on white cardboard: "Blame Palin. Blame the Tea Party".

The 60-something former miner did not wait to explain why. "They're trying to say that a lone nut was responsible for this, but Sarah Palin and the Tea Party might as well have put the gun in his hand. They are the ones who painted Giffords as some kind of traitor," he said.

Wellman did not take much notice of the small woman with the camera watching him from the edge of the car park. After he moved off, she stepped forward.

"There have been a number of these," she said grabbing his sign and declining to give her name. "It's wrong. Why make it about politics?"

Then she carried off Wellman's sign to dump it.

Another sign had already been removed: "Republicans are murderers and un-American".

As much of Tucson unites in keeping watch on the fate of their badly wounded Democratic party congresswoman after she was shot in the head at a meeting with constituents at a shopping centre, and mourns six others, including a nine year-old girl, anger at the shootings is finding very different targets.

Some see the accused killer, Jared Loughner, as a deranged individual acting on his own.

Giffords's father was among the first to point a finger elsewhere. As he rushed to his daughter's hospital bed, 75-year-old Spencer Giffords was asked if she had any enemies. He wept and replied: "Yeah, the whole Tea Party."

Loughner is not telling police why he unloaded his semi-automatic gun into the congresswoman from Tucson at a Safeway supermarket where Giffords was holding one of her regular "Congress on your corner" meetings with constituents.

The 22-year-old asked to talk to the congresswoman and was directed to the back of a line of people before breaking away a few minutes later and opening fire as he moved towards her. He continued squeezing the trigger of his semi-automatic pistol until he was wrestled to the ground.

Police released CCTV footage of a man in his 50s who was believed to have been with Loughner in the supermarket before the killings, but was later ruled out of the investigation. Pima County sheriff's deputy Jason Ogan said the man was a cab driver who drove the gunman to the store and went into the store because he apparently had not paid his fare.

With one eye on the gunman's rambling, disjointed denunciations of authority on the internet, critics said it was difficult to separate the shooting from increasingly menacing tone of anti-government sentiment on the right, some of it targeted directly at Giffords.

Republicans rushed to denounce the attack. Tea Partiers, recognising that their movement might be badly tainted, quickly portrayed the shooting as the work of a lone, unhinged misfit.

But the local sheriff, Clarence Dupnik, said he suspected that the growing vitriol, hate and anger against the government, and the widening rhetoric of armed resistance in the political discourse, played a role in the shootings. The National Jewish Democratic Council said: "Many have contributed to the building levels of vitriol in our political discourse."

The congresswoman, the first Jewish woman elected from Arizona, was a target for Tea Party rage after she voted in favour of what Palin denounced as the president's "socialist" healthcare reforms and opposed what many described as racist new anti-immigration laws in Arizona.

The windows of her office were stoned or shot out, and Tea Party protests were regularly held at which Giffords was denounced as a traitor to the constitution and the country.

Like other members of Congress who supported healthcare reform, Giffords faced vitriolic attacks at town hall meetings by what she would call the "crazies". Across the country, Tea Partiers accused their elected representatives of betraying America, of being Nazis or communists for supporting Obama's attempt to ensure that everyone has access to healthcare. With the rhetoric came the regular allusions to armed resistance.

In August, the police removed a protester who arrived at a constituency meeting held by Giffords after a gun he was carrying in a holster fell out and clattered on the floor. Another activist arrived carrying a rifle, legally, at a protest during an appearance in Arizona by Obama.

During last year's elections, Giffords was among Democrats targeted on Palin's Facebook page through the crosshairs of a rifle. After protests, Palin removed the crosshairs. Giffords was also the target of a campaign advert by her Tea Party-backed Republican opponent, Jesse Kelly, a former marine who served in Iraq, who she beat by the slimmest of margins. "Get on Target for Victory in November. Help remove Gabrielle Giffords from office. Shoot a fully automatic M16 with Jesse Kelly," it said. Kelly appeared on his own website in camouflage gear, holding a gun to promote the event.

Probably unintentionally, Loughner also killed another hate figure when he opened fire at the shopping centre. John Roll was a federal judge who drew scorn and vitriol for ruling in favour of illegal immigrants in a lawsuit against an Arizona rancher in 2009. The police at the time said extremists made serious threats to kill Roll and his family, in part spurred by local talk radio hosts. US marshals put the judge and his wife under round-the-clock protection for a time.

Tea Party leaders are clearly worried by an association with the shootings. Today, Palin offered her "sincere condolences" to Giffords's family and said she was praying for the victims of the shooting "and for peace and justice". Judson Phillips, the founder of Tea Party Nation, said on his website that Giffords was a liberal but "that does not matter now. No one should be a victim of violence because of their political beliefs".

But Dupnik said he saw a link between vicious anti-government rhetoric and the shootings. "When you look at unbalanced people, how they respond to the vitriol that comes out of certain mouths about tearing down the government. The anger, the hatred, the bigotry that goes on in this country is getting to be outrageous," he said. "And unfortunately, Arizona, I think, has become the capital. We have become the mecca for prejudice and bigotry."

Giffords herself recognised the dangers. "They really need to realise that the rhetoric and firing people up, and, you know, even things for example, we're on Sarah Palin's targeted list, but the thing is, that the way that she has it depicted has the crosshairs of a gunsight over our district. When people do that, you gotta realise there's consequences to that action," she told MSNBC last year.

Not all of Giffords's supporters agreed. As Natalie Kujawa – a Democrat who voted for Giffords – laid flowers outside the congresswoman's office, she said that only one man was to blame for the tragedy.

"It was a mentally unstable person. It's terrible but I think if everyone can take the higher road and conduct themselves with a little bit of grace. There's a lot of people who are angry and I don't think that's going to do any of us any good."

Kujawa laid her flowers near a sign that read: "Don't make this about politics. Republicans and Democrats deplore this kind of hatred and violence."

None of that mattered to a young nine-year-old boy called Sammy who arrived at the memorial carrying flowers with his father. He was there, he said, because the young girl who died, Christina-Taylor Green, had been the same age as him. Sammy said he didn't know what to call the circumstances of her death. "It's just very sad that anyone would shoot anyone," he said.

Survival chances

About one in 20 people who suffer a gunshot to the head survive, according to US national statistics. The crucial factor is the extent of damage to the brain, which will depend on the trajectory of the bullet. The most deadly gunshot wounds to the head are bullets that pass through the centre of the brain. In the rare instances that a victim survives this, complications such as swelling, clots on the brain or bone fragments can prove fatal. The bullet that struck Gabrielle Giffords travelled the length of the left side of her brain, from back to front. That may have saved her life. A bullet travelling from back to front generally destroys just one of the brain's hemispheres, limiting the functions lost to the injury. A bullet that travels from side to side is more likely to damage both hemispheres, along with the brain's central core, which controls many of the body's functions.The extent of brain damage suffered by Giffords is uncertain but the bullet struck an area at the front of her brain, which controls speech function and personality. Haroon Siddique