Russian Warning

In March 2011, the Russian security service sent a stark warning to the F.B.I., reporting that Tamerlan Tsarnaev was “a follower of radical Islam” who had “changed drastically since 2010” and was preparing to travel to Russia’s turbulent Caucasus to connect with underground militant groups. Six months later, Russia sent the same warning to the C.I.A.

On April 15, law enforcement officials say, Mr. Tsarnaev and his younger brother, Dzhokhar, set off bombs at the Boston Marathon, killing three people and maiming many others.

Read the full story on the New York Times website…