1) They avoid eye contact.
2) They incriminate their siblings before you even asked what happened.
3) They slide away from you with their backs against the wall.
4) The evidence or traces of evidence is still in their hand/mouth
5) They change the subject by picking at your face.
6) They look up and say, "Ummmmmm..." a lot.
7) They sit on the floor pouting with the occassional arm flap and leg kick.
8) They begin to cry after the hurt sibling cries for you.
9) When you ask, "Who did this?" they SMILE as they point to the innocent sibling.
10) They perform a bodily function as a diversion.