MOSCOW, June 7 (RIA Novosti) – An American team investigating the Boston Marathon bombing returned to Russia's southern republic of Dagestan this week to question the suspects’ parents further, the Associated Press reported on Thursday, citing the suspects’ mother.

This is their second visit to Dagestan in connection with the April 15 Boston Marathon attack in which three people died and over 200 were injured.

Investigators on this visit were mainly interested in finding out what radicalizing influences one of the suspects, Tamerlan Tsarnaev, was exposed to during his brief time in the republic in 2012, his mother told the AP.

Tamerlan Tsarnaev, 26, was killed during a shootout with police on the day of the attack. His younger brother, Dzhokhar, 19, has been charged with conspiracy to use a weapon of mass destruction and is in US custody.

In 2011, Russia asked the US Federal Bureau of Investigation (FBI) to interview Tamerlan Tsarnaev over concerns relating to his interest in “radical Islam.” However, an FBI statement said that it “did not find any terrorism activity, domestic or foreign,” after questioning Tamerlan and members of his family at that time.