I know there are several times in the game, mainly with Carley, Katjaa, Kenny, officer carcrash, etc, where you can talk about your past. Carley brings it up in episode 1 but we don't know what actually happened. Can kinda talk to Clem about it in the drugstore but Lee is purposely vague to her about the details. Again in episode two on the walk to the farm there's more dialogue with Carley. Episode three brings the most info so far where you can tell everyone in the group and some ask questions depending on how you answer (You killed, or you were going to jail). Depending on your response we get bits and pieces of what happened as he explains himself.
What I'm looking for is someone dedicated enough and has some recording device (I would want to do it if I did) to put a collection video of all the pieces of dialogue about his past together, not just a normal playthrough of it but all possible dialogue Lee has about it depending on your choices. Maybe we can once and for all be his judge and jury on what happened :P