I really believe that the murder was committed by more than 1 person. It's not possible for 1 person to have controlled all the family gun or not.
Maybe so,but if a " killer " had been contracted by,say,Jeremy,don't you think that a " payment " of £2,000 was rather small in comparison to the £25,000 which JM received for doing nothing ?? He'd be rather sick don't you think ?
Having said that,the killer was already inside the farmhouse,locked,bolted and shuttered in.