Board Thread:Theories/@comment-30177491-20161008220452/@comment-27441457-20161008221614

Any Titan or Titan Shifter that eats a Titan Shifter with the Coordinate will inherit the Coordinate afterwards. If Grisha fed Frieda to Eren, Grisha wouldn't have died. He most likely couldn't risk taking her alive, where she could potentially transform later and use the Coordinate against him.

Annie would have inherited the Coordinate if she killed and ate Eren, but since she's not of the Reiss or Fritz family she wouldn't be able to use it either. The Warriors are able to take Eren alive with their numbers (though both attempts failed), and if either of them ate Eren they would have to be eaten by someone else (Zeke would be my guess thanks to mama Fritz) before the Coordinate could be usable.