The social fabric of Arizona seems to be deteriorating as fast as the state's population grows, driving it to the brink of dysfunction. The shooting of congresswoman Gabrielle Giffords, US district court judge John Roll and several other innocent bystanders by a lone gunman have brought the state's crisis to the fore, prompting Pima County sheriff Clarence Dupnik to declare it "the mecca for prejudice and bigotry".

Since I first travelled to Arizona more than seven years ago to interview rightwingers participating in armed anti-immigrant vigilante patrols along the border, I have watched as it drowned in a sea of extremism, signing away its future in the form of racist ballot measures and budget-busting tax cuts. In this climate, the assassination attempt on Giffords was not terribly surprising.

My experience began in early 2003 at a propane delivery shop in Sierra Vista, a rural town along the US-Mexican border. I met Roger Barnett, a lumbering 60-year-old former deputy sheriff popular with the burgeoning national anti-immigration movement. Barnett boasted that he had personally captured 12,000 migrants traversing his ranch, held them at the point of a rifle, and turned them over to the border patrol.

Arizona had demonstrated leadership in the field of bigotry as early as 1990, when state lawmakers (including John McCain) refused to honour Martin Luther King Jr with a federal holiday, prompting the National Football League to move the Super Bowl from Phoenix to another city. But as migrant trials shifted from newly walled-off border cities to Arizona's desert, the state became a hotbed of anti-immigrant sentiment. Discriminatory bills aimed at Latino immigrants flew through the Republican-dominated legislature, while extremists from around the country poured into the state to join the Minutemen, a far-right vigilante group inspired by Barnett.

Led by lawmakers such as Russell Pearce, a fanatically anti-immigrant senator who has proudly palled around with local neo-Nazis, the Republican-controlled state legislature refuses to stop cutting taxes on businesses and the wealthy. To plug its whopping $4.5bn deficit, Arizona has auctioned off all its state buildings, including the Capitol and state hospital, to the highest bidder.

A bizarre federal programme, Operation Streamline, helps to pump federal money into the local economy: desperate migrants serve as commodities; 75 of them are marched in chains into a federal courtroom in Tucson each day, compelled to plead guilty en masse to entering the country, then transported to a corporate-owned prison in rural Pinal County before being deported on private charter flights. Several prisoners have died in the jail, including one who was apparently refused treatment while writhing in pain with testicular cancer. But incarcerating Mexican migrants has brought 1,500 new jobs to the previously depressed area, making it one of Money Magazine's top employment growth sites. (The programme costs American taxpayers $11m a month.)

When President Obama took office, Arizona's anti-immigrant right fused with extreme elements of the religious right under the Tea Party banner. In August 2009, a young man called Chris Broughton openly carried an AR-15 assault rifle and a handgun to an Obama rally in Phoenix. The night before, Broughton had attended a sermon called "Why I hate Barack Obama" given by the Rev Steven Anderson, a local Tea Party activist. Anderson declared that that night he was going to "pray for Barack Obama to die and go to hell".

I was summoned back to Arizona in February 2009 to testify as a prosecution witness in a civil trial against Barnett, who was being sued by a group of migrants for physically attacking them while holding them at gunpoint and threatening to kill them. Judge Roll had certified the trial, an act that brought in hundreds of threats against him and his family from local anti-immigrant fanatics, forcing him to live under 24-hour protective guard. He was a conservative Republican, but he was committed to the rule of law.

I told the jury about how Barnett had bragged to me about taking migrants hostage. In the end, the jurors delivered justice, forcing Barnett to pay his victims $73,000 in damages. Roll politely excused me from his courtroom, I did not see him again until his face appeared in newscasts about his killing during the assassination attempt on Giffords.

Roll spent a significant part of his judicial career in Arizona's climate of violent extremism, and he died in it too. He was an innocent bystander, and not the only victim. Unfortunately, he may not be the last one either.

Max Blumenthal is an award-winning journalist and bestselling author