Can my son avoid being expelled if prescription drugs were taken from our home by his friend, with his knowledge, but without having possession?

My son is a junior in high school, and a friend of his were in our house and found prescription Percocet and Valium, of which his friend said they could sell. My son did not think it was a good idea and told him so, but the friend ultimately convinced him to allow him to take a few (we believe about 7, 5 of Percocet and 2 of valium). This was a couple of months ago. My son said he did not want to be involved and did not want any part of holding onto them. A week ago, the kid that was in our house was caught selling them to another kid in school and both of those kids got arrested. My son was called in to the principal for questioning and also got suspended for 5 days on a principal's suspension, but is now facing a superintendent's hearing with the possibility of being expelled for his senior year, which would be detrimental to his mental health, life and future. He is 16 and was not in actual "possession" of anything, however is considered to be the source because he allowed it.