Of course, all of these factors can be found in other states. And many Arizonans cherish their friendships, volunteer at charities and work to strengthen a sense of community, despite all the angry background noise. But that noise is especially pervasive and inescapable here, and perhaps by trying to understand what happened, we can learn something useful. At least, we can be honest about how bad things have become.

Sheriff Clarence Dupnik, the head of law enforcement in Pima County, surrounding Tucson city limits, is a friend of Giffords. He framed the mass-murder in stark terms in an emotional press conference: "I think it's time as a country that we need to do a little soul-searching, because it's the vitriolic rhetoric that we hear, day in and day out, from people in the radio business, and some people in the TV business. ... This has not become the nice United States of America that most of us grew up in. ... 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, and unfortunately Arizona, I think, has become sort of the capital. We have become the mecca for prejudice and bigotry."

Dupnik was almost immediately hounded into silence by a virulent wave of criticism, but many in Tucson felt like he was on the right track. "Every time I hear that this (Loughner's shooting rampage) is just about a single sick individual -- that's so limiting, so naive and almost condescending," says Dan Ranieri, executive director of the La Frontera behavioral health centers in Tucson. "It defines a person just by an illness and it absolves people of their responsibilities. This event happened because of the extremism and the isolation of (people in) Arizona. And you have to talk about both. Nobody is going to convince me that didn't help pull the trigger."

One of the nation's foremost authorities on political assassination lives in a condo barely two miles from the Safeway. James A. Clarke is a professor emeritus at the University of Arizona and the author of On Being Mad or Merely Angry, a study of the psychology of John Hinckley, who tried to kill President Reagan in 1981, as well as American Assassins, a comprehensive exploration of the varied motivations behind many successful and would-be political assassins, from John Wilkes Booth on to the present day. Clarke found that those who plot violence against politicians are generally suffering from mental illness, and are also influenced by the culture at large. They are the product of a specific set of circumstances in a specific time. The idea that the political noise in the autumn of 2010 didn't influence Loughner's decision to shoot Giffords is, Clarke says, "pure nonsense."

"The toxicity of (Giffords' last campaign) was beyond anything I've ever experienced, and I've lived here 30 years," says Clarke. "I don't think the kid (Loughner) had a clear political rationale. It may not have been defined in liberal-conservative terms, but he was clearly anti-government, and the anti-government rhetoric was a major part of the campaign against Gabrielle Giffords." For someone like Loughner, who was spiraling into a paranoid schizophrenic view of the world, "Giffords was the government doing all these bad things." He adds: "All assassins have a history of social disconnection. And the neighborhoods here are some of the coldest and most distant that I've ever experienced."

I know this instinctively, because I grew up in one of those subdivisions, and I have not forgotten the loneliness. When I was 11, in 1980, my parents moved us from Phoenix to what was then the edge of Tucson, into a new subdivision that had a typical arbitrary name, Shadow Hills, about two miles from the Safeway. A Texas megacorporation, U.S. Home, had bought two square miles of desert and bladed streets that ignored the natural contours, with names like Camino Alberca (Swimming Pool Street) and Camino Padre Isidoro (Father Isidoro Street). To this day I have no idea who Father Isidoro was or if he even existed or was just a developer's picturesque invention. On the side of our house was a limbless saguaro cactus that was slowly dying; one of the men who helped build the house had shot it repeatedly with a pneumatic nail gun, so its flank was full of rusting metal and its ribs were rotting from the wounds. There were no sidewalks; I rode my bicycle in endless circuits past other houses that were like locked-up boxes. I knew no one in them, and seldom saw our neighbors except when they were sealed inside their cars.

My junior high school was called Orange Grove, though there were no orange groves anywhere in sight, just more cactus. As a newcomer, I ate lunch alone each day and got provoked into stupid fights. I learned to be on guard constantly, failed quizzes and stopped doing homework, instead watching hours of bad TV shows without any pleasure. My father kept a pistol hidden in a closet, and I found myself wondering what it would be like to shoot myself. After I read The Monkey Wrench Gang, Edward Abbey's novel about a group of desert eco-raiders, I began pulling up survey stakes on the empty Shadow Hills lots and tossing them in the washes, in a fatuous mini-protest against "development." Sometimes I sneaked into unfinished houses and smashed out the windows with rocks, or took lengths of rebar steel and flung them at saguaros, where they made a satisfying, fleshy thunk, and the cactus bled green juice like tears. I had nobody to talk with and even flunked seventh grade. At my high school, Canyon del Oro, I threw myself into the school newspaper. I loved everything about that: the way the page crystallized reality into neat columns; the hard rationality of deadlines; the chemical smell of the ink from the printers; the sense of subversive power that came from being able to lob stink-bomb stories against some administrative outrage or another.

Most of all, I loved the way that the newspaper helped me feel like I belonged, without actually belonging. Taking on the role of a journalist allowed me to float among a variety of activities, watching and summarizing but not participating. The role forced me to talk to people, but I could keep my distance; I didn't have to contribute anything other than a few pleasant questions. The journalist's posture of impartiality was never difficult for me; I dodged commitment to any cause, and refused to believe that I belonged in Arizona. My buddies and I took our parents' cars out and ran over curbside garbage cans, flattening them and scattering trash in the xeriscaped yards like a mini-cyclone. We got arrested a time or two by Sheriff Dupnik's deputies for petty vandalism and other misdeeds. Massive shopping strips were springing up on all the important corners, and I took a job as a burger chef at a Carl's Jr. fast-food restaurant for minimum wage. The spattering from the processed meat left my uniform constantly greasy. I worked there for a year, addicted to the money that bought gasoline.

In search of a horizon I couldn't name, I escaped to a small liberal arts college in Wisconsin, and then I chased full-time newspaper jobs, deliberately changing papers and cities every few years. Eventually, I got hired by The Arizona Republic and moved back to Phoenix. I rented a loft apartment downtown with a view of urban palm trees and walked to work on cracked sidewalks, across the same routes where my grandmother had walked to her elementary school in the 1920s. I lunched with the lawyer-lobbyists who helped run things at the Capitol, often at Mexican restaurants where misters sprayed fogs of water to keep the patios cool. Twice a year, a nonpartisan policy group put on an event called Arizona Town Hall, in which participants in the governing class sequestered themselves in a resort hotel somewhere, to debate some important question. The Republic dutifully covered these confabulations, and when my number came up I was told to go to El Tovar, the historic lodge on the South Rim of the Grand Canyon, to write a couple of brief stories. The assignment was dull, but at a party the second night, I met Jim McNulty, an Irish prosecutor from Bisbee who represented Southern Arizona in Congress as a Democrat for a brief spell in the early 1980s. Sitting next to him was an attractive woman about my age, wearing an open-necked white blouse and a small gold chain necklace. Her hair was whiskey-colored and she had a mildly squeaky voice -- girlish but not unserious. When she laughed at something McNulty said, she squeezed her eyes shut and her cheekbones went even higher. She punched him on the arm with mock disdain. Her hands were small, with slender fingers and short unbitten fingernails. I learned that she was a newly elected member of the Arizona House of Representatives, named Gabrielle Giffords.