Board Thread:Questions and Answers/@comment-25322628-20160319002309/@comment-25322628-20160322233354

Don't forget that Eren just recently learned of his Titan abilities; amateurs are screw-ups, so they're never perfect or precise. You can't expect him to master it all instantly with very little experience.

Any kills that he committed as a Titan can be held against his father, who forced him to become a Titan. He'd be guilty by association only.