First of all my deep regrets to know of this, Istafa bro.
Second, I really admire the lightness with which you're taking this in the way of Allah! Great. Inshallah, this is not your loss, but will be paid back hundred folds, no doubts, Allah is Great!
3rd. If you do not mind, or if I oversaw anything, were you present in the house and those suckers totally "noise-less", or were you out at the moment? This, just to establish the professionalism of these guys.
Finally, when things like this have to happen, they just happen, no precautionary measures are enough and I'm pretty sure you already took those which came to your mind, but this proves one thing at least, that this specific and partially opened window either was known to them in terms of trespassing around your house earlier, or it was just too visible from the open street, whatever.
In any case, I've realized that more than weapons, a good watchdog or 2, kept in concealed area with no approach, and just for the cause of alarm, are good to have.
I myself live in one of these "secure" areas, with provided night security around, but sadly, more than to alert the thieves, I occasionally have to do a couple of fires at night, just to get the security guyz on the feet!!! Lolz! (I've deliberately placed some targets in my lawn for this purpose and use these occasionally, when needed, at night, as to avert the menace of aerial shots and to get the guards walking my street, lolz!)
No suggestions bro, no, just prayers for your fortitude.