Correct spelling could have prevented the Boston Marathon bombing.

A congressional report will reveal that the US missed several chances to detain Tamerlan Tsarnaev after getting warnings about him from Russian authorities.

In July of 2012, less than a year before the bombing, Tsarnaev had returned to America from overseas where he allegedly received terrorist training.

His name appeared on a watch list warning that he could be armed and dangerous and should be detained, but his name on the list had been misspelled as "Tarnayev," with an extra Y.

The report also says the FBI opened and closed an investigation after getting the warning from Russia, but didn't reopen it after a second warning was received.

--Rob Archer