Oh my gosh, that's terrible. Do you have a clause in your contract stating no responsibilty for theft to renter's items? Did they know the system was broken and there was a burglary before? If you had a burglary 1 month before and the security system was broken, I would not have rented it until the system was fixed. It seems your property or neighborhood is being targeted or that they know it's a short term rental. If there isn't a clause, I would be inclined to help pay the deductible since it was something you knew that was possible from the previous break in.
I'm sorry to hear this happened to you and your guests. There was another discussion recently on a very similar topic. Some of the tips be might be helpful to you. Just in case you hadn't seen it, here's a link to the other discussion about theft when guests were in the rental.