It is a familiar type. There are thousands, perhaps hundreds of thousands, of Americans who hold beliefs identical to McVeigh's. He is a prototypical extreme-right zealot: He hates and fears the federal government, worships guns, fetishizes "liberty" (defined in almost purely negative terms, as freedom from external interference of any kind), embraces survivalism and sees himself as having acted in a proud American tradition of resistance to tyranny that goes back to the Founders. Throw in belief in the gold standard, certainty that a U.N.-run "New World Order" is poised to take over the world, racial resentment and an obsessive fixation on Ruby Ridge and Waco as proof that federal agents are jackbooted thugs waiting to make their final move, and the all-too-familiar portrait is complete.

This belief system is not confined to the fringes of American society. It has deep roots in the American psyche. What historian David H. Bennett calls "the party of fear" recurs in many related forms throughout our history, from nativist, anti-foreigner fraternities like the Know-Nothings to the Ku Klux Klan, Father Coughlin's anti-Semitic radio broadcasts, McCarthyism, the John Birch Society, the Moral Majority and Christian Identity. People who subscribe to such views are to be found at gun shows and NRA rallies, in militia groups, on government-bashing Internet forums, in radical anti-abortion groups, at anti-tax rallies, at Klan rallies and holed up in survivalist cabins in the West. They devour "The Turner Diaries" and "The Protocols of the Elders of Zion" and Tom Clancy novels, listen to Jerry Falwell and Pat Robertson and Rush Limbaugh and the hundreds of resentment-spewing right-wing radio ranters all over the country. They avidly read Matt Drudge and fire off angry, often obscenity-filled e-tirades to liberal Web sites, sometimes boasting ominously that "our side has the guns." And, of course, in a more toned-down, respectable form, most of McVeigh's beliefs are shared by the activist core of the Republican Party.

There is a common ideological thread that runs from Timothy McVeigh to bedrock Republicanism, and the shared emotional leitmotif of that ideology is anger. What distinguishes America's worst domestic terrorist from Newt Gingrich, Tom DeLay and George W. Bush is the intensity of that anger. McVeigh and his fellow extremists burn with rage, are consumed and obsessed by it. They are the pathological white-hot center of the right wing. Radiating out from that center, next come the extreme conservatives, the rabid Clinton-haters and Bible-thumping doomsayers, the angry zealots for whom business-as-usual Republicanism is too moderate -- the group normally thought of as the true-believer Republican "base." After this suburb, you cross the city limits into mainstream conservative territory -- and the distinction between the city and the suburb is pretty blurred.

Of course, the critical point is that none of those thousands or tens of thousands of Americans who share McVeigh's rage and radical beliefs -- and those millions who share his general anti-government philosophy -- drove a Ryder truck loaded with 7,000 pounds of explosives to the Murrah Federal Building in Oklahoma City and blew it up, killing 168 men, women and children. Timothy McVeigh did. Hence the question that inescapably hangs over every sentence of this book: Why? What made this particular man, who will be executed in a little over a month, commit the worst act of domestic terrorism in American history?

Reading this book provokes two opposite responses. The first is that we'll never know. No one can unlock a human heart, can fathom why a certain person decides to kill.

The second is that we know for certain why he did it. He was the perfect candidate. He led the perfect life. It all adds up.

Both responses are valid. At some ultimate level, McVeigh's hideous deed remains shrouded in existential darkness. But at a more practical level, it seems completely natural, utterly comprehensible, that this man in particular did it. McVeigh's deed was ignited by his life experience and beliefs as inevitably as a bomb is set off by a lit fuse.

One thing is disturbingly clear: Whatever else he is, Timothy McVeigh is not insane. A psychiatrist, Dr. John R. Smith, who examined him when he was in prison concluded that he was not delusional, or even evil. "Clinically, he saw him as an essentially decent person who had allowed rage to build up inside him to the point that he had lashed out in one terrible, violent act. 'I've seen it many times,' Smith maintains. 'Nice people do really terrible things.'" This evaluation jibes with the portrait of McVeigh that emerges from "American Terrorist." Obsessive, fanatical, single-minded, cold-blooded and very, very angry, yes. Insane, no.

Maya Angelou reads from "The Heart of a Woman"