Russia warned the U.S. about Tsarnaev, but a spelling issue helped him escape

The Russian government warned U.S. authorities that Boston Marathon bomber Tamerlan Tsarnaev was a violent radical Islamist more than a year and a half before the April 2013 bombing, but authorities missed multiple chances to detain Tsarnaev when he was traveling to and from Dagestan for terror training, according to a soon-to-be released Congressional report.

In one instance, according to the report prepared by investigators for the House Homeland Security Committee and copies of documents reviewed by NBC News, Tsarnaev was supposed to be pulled aside for questioning at JFK airport because he was considered potentially armed and dangerous, but he slipped through undetected because someone had misspelled his last name in a security database.

“This sounds like a huge hole and an opportunity missed,” said Ed Davis, who was Boston’s chief of police at the time of the Marathon bombing.

NBC News has reviewed a copy of the report and copies of documents referenced in the report and constructed a timeline that shows how Russia warned the U.S. and what the U.S. did, and didn’t do, in response.