The 1927 executions of anarchists Nicola Sacco and Bartolomeo Vanzetti had important elements in common with the Cold War executions of Julius and Ethel Rosenberg and the espionage conviction of Alger Hiss. All three cases caused an international furor, aggravated domestic political divisions, and provided a rallying point and short-term propaganda advantage for the left. Disputes over the evidence in each of these trials divided scholars, even families, and persisted for decades.

What distinguishes Sacco and Vanzetti from these other cases is that the imperial communist enterprise that fed and cared for the Cold War spies kept a record of its dealings, and during a brief window of opportunity scholars had a good look at the file. The ragtag band of bomb-throwing anarchists Bruce Watson describes in “Sacco and Vanzetti” (Viking, 448 pages, $25.95) were too busy writing manifestos and, well, throwing bombs to keep records.

Another difference is that the jury of history is still out on whether Sacco and Vanzetti were guilty as charged. Defenders of Hiss and the Rosenbergs are getting scarce on the ground, and are limited for the most part to members of the Flat Earth Society, Marxist troglodytes, family, and close personal friends, now dying at a clip.

One thing is certain: Given the developments in criminal jurisprudence between the 1920s and now, it is highly likely that Sacco and Vanzetti would have gotten a second trial. Mr. Watson quotes none other than the late William O. Douglas, a justice of the Supreme Court, who, in 1969, cited the trial judge’s various patriotic exhortations, the manner of jury selection, the identification of suspects without a police lineup, and “the saturation of the trial with the radicalism of the defendants.” Things may have tightened up somewhat since Justice Douglas graced the high court, but not that much.

But history has a different burden of proof than “beyond all reasonable doubt,” and it is clear that if Sacco and Vanzetti did not kill two payroll clerks in Braintree, Mass., they certainly were engaged in plotting to bring down the government of the United States and supported violence to that end. Indeed, their friends and associates were clearly implicated in the string of 1919 bombings that terrorized the nation and prompted President Wilson to launch his controversial raids that rounded up 4,000 aliens, holding many indefinitely without trial, and shipping others back to Europe, which was referred to at the time as a “Soviet Arc.”

It is a tribute to Mr. Watson’s judgment that, while he clearly thinks the pair got a raw deal at trial, he makes no effort to sanctify or even deodorize them. It’s evident from beginning to end that we are a long way from Woody Guthrie paean, not to mention Edna St. Vincent Millay, John Dos Passos, Upton Sinclair, Katherine Anne Porter, and on and on. It’s a long list, and, yes, even Eleanor Roosevelt got into the act.

As to the actual guilt of his anarchists, Mr. Watson remains deeply ambivalent:

If they were innocent, why did Bullet III and Shell W implicate Sacco? If these were substituted, could such a crime be kept secret for so long? What were the men reallydoing, armedtotheteethon the night of May 5? If they were rounding up radical literature, why didn’t they hide the radical literature in their own homes? Why did their roundup wait until five days after Vanzetti returned from New York with warning of imminent raids?”

It’s clear that serious people — not the political tourists listed above — believed the pair innocent of the crimes charged. Eminent jurists such as Felix Frankfurter risked their reputations to publicly defend them. Historians such as Arthur Schlesinger, who would later give hives to the totalitarian left, were at least sympathetic. At the same time, Abbot Lawrence Lowell, then president of Harvard University, headed the commission that confirmed the judgment of the trial court.

It’s a rich cast of characters and Mr. Watson makes the most of it — from radical defense attorney Fred Moore, who keeps marring and then discarding his secretaries, to the ultimate hanging judge, Webster Thayer, who didn’t care much for “anarchists.” H.L Mencken, Heywood Broun, Robert Benchley, Samuel Gompers, and even J. Edgar Hoover take brief bows. And “Sacco and Vanzetti” has almost a quaint feel with its brief attentions to the Wobblies (Industrial Workers of the World), the suffragettes, and the anarchists themselves, with their strange idea that men really are angels and would learn to behave themselves if only government were abolished. Sacco and Vanzetti could have saved themselves a lot of trouble if they had read fewer radical pamphlets and more Federalist Papers.

The saddest part of Mr. Watson’s story is a long epilogue he didn’t include: The frothy idealism of the left in the early years of the last century and its slow, painful descent into the charnel house being prepared by Lenin and Stalin. But then the worst consequences are often the unintended ones.

Mr. Willcox last wrote for these pages on Robert Dallek’s “Nixon and Kissinger.”