Storm,
I thought I would throw in my 2 cents here. I have read several other posts, and seen where some have been plagued with something killing their birds, when the cage wire was very small, and no way that a larger animal could get in. I wonder if this is the culprit in some cases. I did not see where you gave any coop statistics, so I do not know if this fits your scenario or not, but think you will find this interesting as I did.
My grandma used to talk about weasels,attacking her chickens. I live on the same farm she did, and I thought she was crazy, as I was outside in the woods most of the time, and had never seen one. I am 42 now, and saw my first one about 4 years ago, and have not seen one since. I was on my tractor, and hauling a bale of hay. I noticed a dead mouse in the gravel, in the center of the road. On my return trip, I saw this little white thing, that ran like a snake, lol with a serpentine gyration, grab the dead mouse and run with it. It looked like an otter, but only very small, and pure white. The mouse was a small one and the "white thing" was not much bigger. I later learned it was a weasel.
You do have them in Texas. Here are a couple links. The one from Missouri gives a better physical description, and the one from Texas documents that they are where you are at. Hope this sheds some light, it did for me! The one from Texas, look on page 11.
http://www.tpwd.state.tx.us/publications/pwdpubs/media/pwd_bk_k0700_0517.pdf
http://mdc.mo.gov/hunt/furbear/index.htm#weasel
