In his opening statement on Wednesday, a US attorney argued that the man accused of shooting an Arizona-based Indian gas station owner, Balbir Singh Sodhi, four days after the September 11, 2001, attacks was acting out of rage and that his mental illness was to be blamed for his action.

Dan Patterson told jurors that Frank Roque heard relentless voices telling him to "kill the devil" before he shot and killed Sodhi.

Whether Roque, 44, is convicted and sentenced to death in the six-week trial depends largely on whether the jurors believe he was insane when he pulled the trigger of a .380 semi-automatic handgun with deadly accuracy, hitting the Indian immigrant with all five shots.

After the US invasion of Afghanistan and terrorist hunts in retaliation for the 9/11 deaths, "the whole world is watching to see what kind of punishment will they do to their own terrorist?" said Harjit Singh Sodhi, one of the victim's brothers.

Patterson argued that Roque is not a terrorist and that the "patriotic fervour" that followed the terrorist attacks, coupled with Roque's undiagnosed mental illness, were catalysts for the murder.

In a packed courtroom and with Court TV filming the trial for a five-episode report, Patterson said Roque was profoundly affected by the terrorist attacks.

"Frank Roque is mentally ill. He no longer hears the voices he heard on September 11, 2001," Patterson said.

"They've been stilled because he is on medication."

Apparently alluding to the fact that Osama bin Laden wears a turban, Deputy County Attorney Vince Imbordino said Sodhi, 49, became the unfortunate target of Roque's rage because he wore a turban as an expression of his Sikh religion.

"It's a clash of different cultures that came to a deadly end," Imbordino said. "To some extent, this case is about September 11, but I think the evidence will prove it was a flashpoint. It goes much deeper."

In a series of racist statements that began when the World Trade Centre collapsed, Roque announced his murderous plans and told a coworker that he had been treated rudely at a gasoline station on University Drive by "a towel-head or a rag-head", Imbordino said.

He told an Applebee's restaurant employee on September 11: "I'm going to go out and shoot some towel-heads," the prosecutor said.

According to Imbordino, Roque told the coworker that "we should round them all up and kill them. We should kill their children, too, because they'll grow up to be like their parents".

But Patterson said Roque was not racist and had never made racist statements before the September 11 attacks.

"There was a great deal of anger in our community about the terrorists," he said.

Patterson said Roque was never diagnosed as mentally ill before the slaying of Sodhi during a 15-minute shooting spree through east Mesa, in which drive-by shootings were also committed at a Lebanese-owned gas station and an Afghan immigrant's home.

But Roque's mother was twice hospitalised for schizophrenia and there is a genetic predisposition to the disease, Patterson said.

Three of four doctors who examined him found he suffers from a serious mental illness, which sheds light on his history of odd behaviour, he said.

Roque ignored pleas from family members to seek treatment after the September 11 attacks, he said.

Sodhi immigrated from Punjab in 1989 and worked as a cabdriver in the Bay Area until he opened his Chevron station at 80th Street and University Drive in early 2001.

Imbordino said Roque shot Sodhi as he spoke to a landscaper about a leaking hose.

Landscaper Luis Ledemsa testified that he was crouching when he heard a truck's skidding tires. Sodhi's last words were "don't kill me" before shots rang out and the victim collapsed, he said.