Safety glass will most always look the same no matter how or where it shatters, mainly due to the design of the glass. It's made to break into a thousand little pieces (you'll still find pieces five years from now if you still have the car ... they just get everywhere).
I don't think you'll ever be able to conclusively figure out, with 100% surety whether this was weather or some type of sabotage going on. Here are some things to look at which may help you figure it out:
- Is there a foreign object inside the car, like a rock or brick or something which shouldn't be there? If so, you can almost be sure there was foul play.
- Was there anything missing? If there was stuff missing, this too would lead you to believe there was foul play.
- Was there any other windows in the neighborhood which were broke?
- Do you know of anyone who is mad at you?
If you cannot conclusively link any of the above questions to this incident, you almost have to assume it wasn't foul play, but more than likely some other cause. Remember that safety glass is pretty tough stuff, but as you can tell, it's not unbreakable. Glass is strong, but very susceptible to stress risers. If pressure were applied in just the right direction at the right time in conjunction with the stress of the recent hot/cold cycles, this may have happened. Safety glass will not crack alone, it will shatter. That's its nature and how it's designed.
You can never rule out what kids will do, but they will almost invariably leave behind something, be it a rock or something else hard. They won't stick around to pull it out. They will try to be as far away as possible when they do it so as to attain a quick getaway. If it were a thief, stuff would be missing. Take a good look inside your car, I'm betting it will tell you the tale.
