Åsne Seierstad begins her exhaustive account of her country's darkest day since World War II with a moment-by-moment description of Norwegian teenagers fleeing, trying to hide, pleading but ultimately dying, one after another, as a young man in a police uniform calmly and methodically shot them at close range.

"A girl whispered: 'No … ' in a low, scarcely audible voice as she was shot in the head. Her drawn-out 'No-o-o' faded into silence."

Anders Breivik, not a foreign terrorist but Oslo-born and raised — to Norwegians' horror, "one of us"— murdered 69 young Norwegians that awful day. He executed them as he roamed Utoya, island home to the Norwegian Labor Party's annual retreat for leaders of its youth wing. He did this after exploding a car bomb outside government buildings in central Oslo, killing eight.

In Seierstad's stark beginning, there are no names, not for the shooter nor for the young people he shot. We don't know the name of the girl who whispered "No …" or the boy nearby who uttered a feeble "I'm dying," as if he was remarking on the oddity of it.

The anonymous inventory of murderous violence is awful enough. But in the pages to come, we do learn the names and the life stories of some of the people who died on Utoya that day: Simon Saebo, the handsome, caring and outgoing boy from the North, just days shy of his 19th birthday; Bano Rashid, who as a small child fled Iraq with her family and now at 18 was leader of the Labor Party's youth group in her home district. We see them and others. We learn their dreams. We meet their parents, and in time we feel their families' grief.

Through more than 500 pages, the veteran war correspondent and author of the international bestseller "The Bookseller of Kabul" reports trial testimony, public records and interviews with surviving witnesses, Breivik's parents and many others. Like all of Norway, Seierstad gropes for answers. Why did this young man, in many ways a beneficiary of a society where, as Norwegians like to say, "few have too much and fewer have too little," become a mass murderer? She examines his mental and family history, the likely sources of his hostility toward the Labor Party and especially its embrace of feminism and defense of immigration. She examines his dedication to save his homeland from multiculturalism.

But she also documents the nation's strong, unified response to the horrific assault, given voice by Prime Minister Jens Stoltenberg at a national memorial service. "We are a small country, but we are a proud people. We are still shaken by what has happened to us, but we will never relinquish our values. Our answer is more democracy, more openness and more humanity. But never naivety."

Chuck Haga, a former Star Tribune reporter, lived in Norway in 1978-79.