Carlos Kleiber, 74; Brilliant, Reclusive Conductor. Carlos Kleiber, a conductor of tremendous mystique who had the uncanny ability to animate the smallest details in a piece of music yet whose personal elusiveness made him one of the most enigmatic stars of the classical music world, has died.
First of all, it's not illegal to kill a cat or a dog as it's an unfortunate reality for the ones who end up at the humane society or are put down due to illness. Animal cruelty however is illegal and most states have statutes w/ minimum punishments for those caught and convicted.
Depending on where you live, burying your pet in your yard may be illegal. You should check your local laws, before undertaking a reburial. If the area is in a neighborhood, the possibility that a neighbor's dog may find and remove your pet is very high, given the depth the you describe.