So sorry but just remember you didn't kill your chicken. They are suppose to be grazers and foragers and sometimes freak stuff happens. I Keep mine on pasture and never had this happen so Not Your Fault.
Please don't allow guilt to compound the grief you are dealing with. It was a crazy combo of conditions and circumstances that killed little Murphy, not you.
We can all show you a long list of much loved chickens that have died in spite of our efforts to save them. The only consolation is that each death has taught us a bit more that might help save future chickens in our care.
You will miss Murphy, but the pain will get a little less intense each day.