Boston Marathon bombings investigators are examining whether suspect Tamerlan Tsarnaev was influenced by Magomed Kartashov, a distant cousin with ties to extremist Islamist groups in Russia.

Magomed Kartashov is founder and leader of a group called The Union of the Just which reportedly promotes the application of Islamic Sharia law and has protested against the U.S.

Tamerlan Tsarnaev is said to have met Magomed Kartashov for the first time when he spent six months in Dagestan, Russia’s turbulent Caucasus region, last year.

His mother, Zubeidat Tsarnaeva, told TIME Magazine that the two “became very close”.

Magomed Kartashov is founder and leader of a group called The Union of the Just which reportedly promotes the application of Islamic Sharia law

The Union of the Just publicly renounces violence, but several of its members have ties to militants.

A lawyer for Magomed Kartashov confirmed to ABC News that Russian security agents recently interviewed her client about his links to Tamerlan Tsarnaev.

Magomed Kartashov admits that the two were close but insists that it was Tamerlan Tsarnaev who tried to “pull him into extremism”.

He is currently in jail on charges of resisting police in an unrelated matter. His lawyer expects he will remain there for at least two more months.

Tamerlan Tsarnaev, 26, was killed during a violent standoff with police on April 19, days after he and his brother Dzhokhar, 19, allegedly planted homemade bombs at the finish line of the Boston Marathon.

Dzhokhar Tsarnaev was captured alive and has been charged with using and conspiring to use a weapon of mass destruction. He faces the death penalty.

Ever since the attack, investigators have been trying to understand how the brothers would have become radicalized to the point of wanting to kill and maim people in the U.S., the country they called home.

Much of the focus has been on Tamerlan Tsarnaev’s six-month visit to Dagestan, a restive region in southern Russia that is home to an Islamist militant insurgency. They want to know if and how Tamerlan Tsarnaev attempted to join militant groups there.

Earlier, a U.S. official confirmed to ABC News that investigators are also looking into Tamerlan Tsarnaev’s contacts with a young militant named Mahmud Mansur Nidal.

The two were reportedly seen leaving a controversial Salafist mosque in the capital of Makhachkala that has been popular with militants over the years.

They also want to know about possible contacts with a Canadian-Russian militant named William Plonikov, who was killed in a police shootout last July, just days before Tamerlan Tsarnaev suddenly left the country.

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