User blog comment:NickFusi0n/A Theory on The Coordinate and The Wall Titans/@comment-3074300-20140524172812

After a bit of thinking I came up with another theory - Grisha Jaeger is from the same town as Reiner, Annie and Bertolt. He moved into the walls before the whole "Let's fuck up humanity" plan was in motion. Following up, being a Titan Shifter passes down through family, therefore, Eren was already a Titan Shifter. So what did Grisha inject him with? The Coordinate. Then he disappeared. He most likely stole it from the town and took it away with him because he was against their plan to kill off humanity using it. (This also follows up part of my previous theory for the Coordinate being used to force the Wall Titans out of the walls and bring them down). Grisha knew the town was after him so he gave Eren the Coordinate and dissapeared. All of this information, if true, should likely be in the basement for Eren to find out. And if you payed attention to the scenes that did show Grisha Jaeger, you would notice that he always did look a little sad and down. Probably knowing that his time is coming, he gave Eren the Coordinate and after the injection he disappeared and either hid or was killed by the foreigners. Either that, or he lied to protect Eren, saying that he injected the Coordinate into himself. Then they had another Titan eat him, in hopes of that Titan turning back into a human and having the Coordinate. But when that didn't work, they realized he lied.

Think about it, it would make sense. Plus it fits more with the "If you want to save Mikasa, Armin and everyone else you must master this power!" line.