In what could be a breakthrough in the attempt to understand how Tamerlan Tsarnaev – himself a skilled boxer – became radicalised and turned to violence, Moscow's respected Novaya Gazeta newspaper revealed his links with William Plotnikov, who was killed in a battle with security forces in the troubled southern Russian republic of Dagestan last year.
During his visit to Dagestan last year, Tsarnaev also met on several occasions a terrorist of mixed Dagestani and Palestinian parentage, who was being closely watched by the Russian security services. That man, Makhmud Mansur Nidal, had been under surveillance for six months as a suspected recruiter for Islamist insurgents fighting Moscow's rule in the region.
Tsarnaev, 26, died during a shoot-out with US police in Boston on April 19, and his brother Dkhokhar, 19, was hurt and eventually captured. The two allegedly detonated bombs near the finishing line of the Boston marathon four days earlier, in a devastating attack that killed three people and wounded more than 260.
In the investigations that followed there have been few clues as to who played the key roles in radicalising the older Tsarnaev brother, who is thought to have taken the lead in instigating the Boston attacks.