Could Damon be innocent?
It is possible that another vampire used his mind powers to make him think it was Damon who killed Alaric wife. He doesn't have many fans and it does seem like allot of people hate the Salvador brothers and knew Katherine quite well. Perhaps they may have even been jealous or even blame Damon for what happened to Katherine.
If it turns out that Alaric is Elena's father or his wifes child then things could get quite sticky. I guess we will have to wait to see what Damon says about it when it all comes to light, but I wouldn't be surprised if Damon didn't do the deed as it would kill any chance of him been with Elena or Bonnie.