Make it a criminal offence to allow a dog to kill/injure another dog

My daughter's dog Bailey was savaged and killed by a Staffordshire Bull Terrier who was not on a lead while Bailey (who was a 24 weeks old Beddlington Cross Beagle) was out walking with my son in law on a public field in Stockport. The police are not interested as a human wasn't injured and the dog warden, will visit the owner and advise them to wear a muzzle and to keep the dog on a lead. Meanwhile, my daughter and son in law have lost their beautiful little puppy Bailey. The law is wrong. Please help get justice.for little Bailey. Help make it a criminal offence to allow a dog to kill or injure another dog so that the owner feels the pain that my daughter and son in law feel.