A possible scenario with Beatrix Kiddo, 
Alibi : Check ! She had taken care to book a round trip to Italy where she also had a friend ready to cover for her who works at an hotel where she had booked a room as well.
Weapon : Check ! The revolver that she had ordered on the dark-net a few weeks before via the false IP address that she had obtained was soundless.
Timing : Check ! He was supposed to leave for Tadjikistan in just 5 months. Nothing would suggest that care had been taken to kill him beforehand.
Plan of attack: Check! She had found a way to obtain the entrance doors to the building where B. lived, thanks to a person found on an obscure platform who had filmed the comings and goings of the residents there. As for the front door of the main person concerned, she had inquired via this same person about her model and had found, thanks to a tutorial, a way to force it using a master key made for this purpose. As for the surveillance cameras, not a shadow of one, she had made sure of that too, with the methodical precision that someone who has been the subject of a serious betrayal can have... Yes, this old building was a bit like the exception that proved the rule, in this hyper-secure neighbourhood that had become gentrified.
So she would wait for him at the end of the afternoon in his little renovated kitchen. Redone, he was going to be, too. She would wait for him there after he went to his daily gym session, to give himself the impression that his life wasn't completely meaningless, between an unhappy marriage and sex, alcohol and drugs addictions, to compensate for the frustration of a life thrown out in grazing ground.
