who drew on the wall?

As we were rushing out for church this morning, Mommy discovered some fresh crayon doodling on the wall next to the easel.
M: Who did this?
B: Meimei did it. She drew on the wall.
M: Not possible.
(Mommy dragged Kristin to the wall and stretched out the little girl's arm. Kristin couldn't even reach the drawing. And then she did the same with Bryan. It was the perfect height. Daddy grinned and commented that it was CSI Frankfurt.)
M: See, it must have been you. Meimei isn't tall enough.
B: But Mom, it's not me. It's Meimei.
M: Ok, since I didn't see it with my own eyes, I will not cane you this time round. But you will still receive punishment because you didn't tell me when you saw Meimei drawing on the wall. So you will have to clean up the mess.
(Mommy passed him an old toothbrush with a little toothpaste on it and got him to scrub off the doodling. By the way, this is a sure way to get crayon stains off the wall.)
M: And the next time when this happens, Meimei will be canned once for drawing on the wall, and you will get canned twice for watching her do it and tell Mommy nothing about it.
B: Ok, Mom.

Yap, you will be punished twice as severely for witnessing a crime and not reporting it. He was obviously being dishonest but I didn't catch him red-handed.