Heather Ann Thompson pries loose the long-kept secrets of Attica in her new book

A few years into researching her book on the 1971 Attica prison revolt, the bloodiest in the nation’s history, Heather Ann Thompson got a lucky break.

In 2006, a clerk at the Erie County Courthouse in western New York let her into a back room, where a wall of jumbled shelves held thousands of documents detailing some of the most closely guarded aspects of the case.

There Ms. Thompson discovered the confidential memo from secret meetings where Gov. Nelson Rockefeller, who had ordered the violent retaking of the prison that left 39 prisoners and hostages dead, sat with police and prison officials to hammer out the state’s official version of the story. She also came across sealed grand jury records, along with a copy of the never-released report from a whistle-blowing prosecutor who had come to believe the state’s investigation was a cover-up.

The papers contained “a great deal of what the state knew, and when it knew it,” as Ms. Thompson puts it — not least, about whether members of law enforcement had potentially committed murder in the retaking.

Even before publication, Ms. Thompson’s book, “Blood in the Water: The Attica Prison Uprising of 1971 and Its Legacy,” released on Tuesday by Pantheon, had drawn criticism for printing the names of some of those officers, who were not indicted and may still be alive.

But the book has also been praised by reviewers and insiders alike for the way it brings together a multitude of sources, finding the clearest path yet through the maze of competing narratives and official secrets surrounding Attica.

“Heather has really crashed through the state’s stone wall of withholding as much as they could,” Malcolm Bell, the former prosecutor who later accused the state of a cover-up, said. “She really covers the whole saga from A to Z, and tells the most human story of Attica that I’ve seen.” ...