Journalist Masha Gessen is not afraid of making news that makes waves. In her bestselling book on Vladimir Putin, she wrote that the Russian FSB bombed Moscow apartment buildings in 1999 and then blamed the bombings on Chechen separatists. Talk of ‘false flags’ usually lands on deaf ears in the United States, but Gessen, who regularly writes for mainstream US outlets like the New Yorker, New York Times, and Washington Post, told a Telegraph reporter that she’s “probably the least conspiratorially minded person in this country of conspiracy theories,” referring to her home country, Russia. Gessen’s conclusion about the Moscow bombings was published widely in the western press. But according to the Telegraph report, the news that the FSB bombed civilian apartment buildings and blamed it on its enemies never really took hold in Russia.

In her new book, Gessen has some similarly uncomfortable things to say about events related to another terrorist attack: the Boston Marathon bombing. Reviews of her book about the Tsarnaevs, “The Brothers: The Road to an American Tragedy,” are starting to appear in the US press this week. The more prominent of them completely ignore what is arguably the book’s most newsworthy section, which the Kansas City Star, breaking the mold, centers in its review.

Gessen, reviewer Kevin Canfield writes, “suggests that Tamerlan Tsarnaev may have been an FBI informant, and that the bureau, desperate to hide its collusion with a man who committed a terrorist act, might have taken extraordinary measures to ensure that other law enforcement officers never got a chance to question him.”

Gessen’s thinking goes like this: Because the FBI questioned Tamerlan Tsarnaev in 2011 and monitored him and his family, agents would have been likely to recognize him in surveillance camera images captured at the site of the bombing, which killed three and injured hundreds. Nonetheless, she writes, agents with the FBI’s Joint Terrorism Task Force didn’t initially identify the Tsarnaev brothers.

“A … logical explanation,” Gessen argues, “is that the person or persons who were in a position to recognize the brothers were consciously concealing this fact in order to protect their own or the agency’s reputation — either because it would look like the FBI had fumbled a solid investigative lead, causing tragedy, or worse, because the FBI had considered Tamerlan an informant.”

Even more incendiary is her suggestion that the FBI deliberately kept police at arm’s length as they were pursuing the brothers “because it needed to ensure that no other law enforcement got to Tamerlan Tsarnaev before the FBI had captured — or killed — him. In other words, the explanation that best fits the facts is a cover-up.”

Facing questions from reporters and a high-ranking US republican senator, the FBI has denied that the brothers were informants.

Gessen’s book will be available on April 7.