Something killed/eviscerated mycat and 8 wk old kitten. they were found INSIDE my horse trailer!!?

Two nights ago my cat and her 4 8 wk. old kittens were inside my horse trailer...There is a window with a grill on it that the mommy cat squeezes thru to come and go...anyway, the next morning one of the babies was just gone...vanished. I thought maybe mommy just moved it...now i know that wasn't the case!I brought the other babies (good size) inside the house for safety, but last night mommy meowed to go out so I let her. This morning I was looking for the missing baby and i opened the door of the horse trailer and found the mommy cat dead. her face was kind of messed up but the most disturbing thing was that whatever killed her totally eviscerated her. all her insides were eaten away. WHAT THE HECK got INTO my horsetrailer thru a 3" opening and did that? I know Tomcats will kill kittens but I didn't think they'd get a mommy cat? Also, we have seen some raccoons around the place after dark. My neighbor saw a snake last week...I'm really creeped out and sad!