Can’t prove it. Reasonable doubt. For example, Casey Anthony could have escaped from jail, taken the water from the swimming pool and handcrafted each drop of water into a six-sided snowflake, stuffed it all into black garbage bags and gently laid the white stuff all over the ground while you slept. Doesn’t matter that it was 82º that night. She may have had an accomplice—Santa Claus and his reindeer.
If a child is thrown in the woods and rots into a skeleton is it still a murder?