User blog comment:Sookey5/Annie is Dead/@comment-24930713-20150817212805/@comment-24930713-20150817220218

Why would it matter, all Titans were once human; and technically still are since eating a shifter gives them the ability to become human again. And we've already seen the most likely way for a Titan shifter to gain the hardening ability. If regular Titans, for some weird unknown reason, have the hardening ability. Then by default Eren should have had the hardening ability from the moment he became a Titan. Since he didn't, it's more likely that Titans in the walls are shifters. That being said, they have likely reached either a near mindless state or remembered everything and been extremely upset.