Lerman might be better known for lighter fair like the Percy Jackson franchise, but he is definitely a gifted actor, as his performance in The Perks Of Being A Wallflower proved. Those roles might be more heroically and sympathetically aligned, but that might actually work well as conscious misdirection. The apparently nice guy without a history of violence is always the least likely to have committed the crime, and as Ed Norton proved way back in Primal Fear, and that archetype could offer the model for an actor of Lerman's make-up to succeed. There is nothing to suggest that the Joker wasn't a sympathetic character before his transformation, or before the necessity for crime awoke something in him that fundamentally changed him from nice to deliciously naughty. Gotham is unlikely to stick too closely to the source material of the comics, with a broader look at some of the important events in Bruce Wayne's early life, and it would probably serve the show well not to be too close to the movies that already exist, for fear of comparison by proximity. The idea of casting someone who seems to be the polar opposite of everything that the Joker represents isn't a bad one at all, as long as the twist revelation, when it eventually comes feels like it's been executed well. In fact it's a quite logical route to go with much like Dr. Jekyll/Mr. Hyde, which could eventually tie up loose ends in who the Joker really and truly is at his core. So imagine Lerman playing a good boy who eventually loses his way to crime out of an act of desperation.
