The "Not Me" gremlin strikes again!

Joel is quite honest when he gets caught about the mischief he has been up to. He will sometimes try to hid when he is doing the deeds, but once caught he usually confesses. He confesses for Evan, too, which is immediately met with a cry of, "No, I didn't!" by Evan.
This past week, I noticed something new about Joel's hair when I got up one morning. It had some holes in spots. Joel admitted he cut it and then added that Evan helped. Of course, Evan denied this vehemently.
Later in the morning, I noticed that there holes in the back of Joel's head of hair, too. I asked Evan how he thought Joel could have cut his hair in the back by himself, and he said sheepishly, "I don't know." Joel immediately chimed in, "Evan did the back." Evan continued to look sheepish and neither confirmed nor denied. In this case I believe silence truly was consent.
I cut the boys' hair that day to try to make it better. There are still noticeable bald spots, but it is some better. I cut Evan's as well, because he knew better than to do that. I told him that his hair would be cut as short as Joel's since he helped with the cutting. Since he hates for me to cut his hair, I am hoping that was enough of a lesson for him.