My son may have stolen drugs from our house?

Someone stole a large quantity of prescription medication from our house on more than one occasion. The only 3 people who had access to our house while we were out of town were my son, his wife, and a friend. My gut feeling tells me that my son (in his 30s) is responsible. I'm not sure how to approach him about it, and am sure he would deny it if I asked. I can get by it, but my husband (not my son's father) is not as likely to forgive him. I'm not sure how to handle it.