In developments Monday in the Boston marathon bombing investigation, Russian special forces killed two members of a jihadist group during an early morning raid in Dagestan, a semi-autonomous republic in southern Russia, two Russian police sources told CNN.

One of those killed, Shakhrudin Askhabov, was a close associate of Abu Dujan, the islamist group's leader.

Nick Paton Walsh reports on the death of Shakhrudin Askhabov, a close associate of Abu Dujan, and possible 'tangential links' to Tamerlan Tsarnaev.