Mr. Tsarnaev said his son had at least once visited the mosque on Kotrova Street in Makhachkala, known for being one of the few places in Russia that openly preaches Salafism, a puritanical strain of Islam centered in Saudi Arabia that has risen in popularity in Dagestan.

WSJ: Boston Suspect Tamerlan Tsarnaev's Dagestan Visit Scrutinized

And at the corner of Fournier Street stands the Jame-e-masjid mosque.

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