Well supposedly: L burned down his own house. It's also possible that the reason as to why he freaks out whenever someone touches him is because he was possibly abused as a child, and when and if he burned his house down he could've killed his parents, making him an orphan, and thus is why he was sent to Wammy's House in the first place.
Well there are also supposed to be 2 more books. The last one I've heard delves more deeply into L's past. Do you remember in the episode of Death Note when those videotapes supposedly sent by Kira are sent to Sakura Television, and then Ukita dies, and Aizawa grabs L's shoulder and L freaks out. Well the author is going to explain why L freaks out whenever someone touches him.