MAKHACHKALA, Russia (AP) — Russian agents placed the elder Boston bombing suspect under surveillance during a six-month visit to southern Russia last year, then scrambled to find him when he suddenly disappeared after police killed a Canadian jihadist, a security official told The Associated Press.

U.S. law enforcement officials have been trying to determine whether Tamerlan Tsarnaev was indoctrinated or trained by militants during his visit to Dagestan, a Caspian Sea province that has become the center of a simmering Islamic insurgency.