but the questions are what did he do, where did he go, whom did he meet. what we do know is when he returned to the u.s., he opened a youtube account, posting increasingly militant islamist videos, including one from this man, abu dujana, a self-styled jihadist leader from dagestan. and he is associated with this man, duku umeroff. this man has been dubbed the osama bin laden of chechnya. he as vowed to attack not just russia, but the u.s. importantly, his group has denied any responsibility for boston marathon bombings. it's not known whether tamerlan ever met with dujana or umeroff. as the investigation continues, a number of open questions have been raised. could tamerlan have met either of these men? did he learn gun handing or bomb-making from them or any of their foot soldiers? until now, there has been no