Last summer Face my Rott got hold of a neighborhood cat who was wearing a collar i guess it was the neighbors behind us, anyway i saw him shaking him violently in his mouth & then Senorita tried to join in, luckily i got out there in time and he dropped it when i yelled at him, and the cat ran up a tree the poor thing was afraid to come down for a loong time, but i know how u feel kinda cuz if they had killed the cat i would of been devastated, we have a lot of strays around and i really have to watch my two cuz they come into our yard once in a while.
It isnt your fault , they're all still animals and will do what animals do.