The report compiled by the House Homeland Security Committee said that even though Russia brought Tsarnaev's terrorism risk to the FBI's attention, he slipped through security measures because of a spelling error.
After the U.S. received word of Tsarnaev's terrorism background in 2011, the FBI questioned him and he was put on a "hot list," which would trigger an alert whenever he left or entered the country. The investigation was closed months later because authorities weren't able to definitively tie Tsarnaev to terrorism, but was re-entered into the system in September 2011 and mandated that he be detained if he traveled to or from the U.S.
However, when Tsarnaev traveled from JFK airport in New York to Moscow, no alarm was sounded and that was because the person who re-entered his name into the system spelled it "Tsarnayev" instead of "Tsarnaev."
"The spelling variants of his name and the birth dates entered into the system -- exactly how the Russian government had provided the data months earlier -- were different enough from the correct information to prevent an alert," a U.S. official told the New York Times.
Tamerlan's brother Dzhokar is on trial in Boston and, if convicted, could face the death penalty.
[New York Times]