It's like my son who would sneak candy and throw the wrappers behind his dresser instead of in the trash. We always found them and my only question was why he didn't throw them away - we would never have known. Shrug!
At least your son was guilty. I kept finding Little Debbie wrappers on our den floor. I thought our sons were covering for each other and I fussed at them almost every day about being pigs.
It wasn't them. I finally caught our cat tossing Little Debbie treats to the dogs from the top of the refrigerator.