athena67a

R.A.B is Sirius brother who was killed by voldermort after discovering the horcrux. The locket is in the possession of Kreacher and Dumbledore is alive somewhere, not only is Snape capable of it as you mentioned but remeber in book 6 just before he dies he tries to convince Draco that he can protect him and his whole family from death (inplying that he can hide them IN DEATH) I believe that Snape is trying to protect and train Harry to be able to kill Voldemort in all that he has done.