What law states the second person gets caught instead of the first?

For example, Bill throws the paper airplane across the classroom without the teacher noticing. The teacher turns around and finds Jim holding the paper airplane, ready to throw it. Jim gets detention instead of Bill.

I was just curious. Is there a law that states that?

Not covered in law, covered by school policy.

However, a general concept in law is that the fact that someone else committed the same crime and was not caught does not excuse others committing the same crime.

guilt by association