Friend implicated Tamerlan Tsarnaev in Waltham slayings, documents show

Federal officials disclosed for the first time publicly late Monday that Ibragim Todashev, a friend of Tamerlan Tsarnaev, told investigators that the deceased alleged Boston Marathon bomber participated in a triple murder in Waltham in 2011. Todashev was killed by an FBI agent who was interviewing him in May. His death remains under investigation. Federal prosecutors confirmed in court records Monday that, “according to Todashev, Tamerlan Tsarnaev participated in the Waltham homicides.” But prosecutors refused to elaborate on their statement.