Shooting birds in gardens using air rifles

Having found several bodies over the last week (shot birds e.g. collared doves), I finally heard the shots this afternoon (Sunday, 24th July), and watcheed, to my horror, as a dove was shot in the tree in the garden next to me.  I was horrified and shouted out. i have reported this to the police and knocked on neighbours doors - all deny knowledge.  I have pets of my own and can't bear to think of this evil people committing this wanton destruction, and possibly aiming also at my pets... what else can I do????