I'm in a slightly similar situation, except I wasn't caught with the marijuana.
Y'see, I had a Sentri card and currently lived in Mexico with a roommate. He's the one who uses it, not me, and as such has no Sentri. A year ago, I hitched a ride with him back to America. At the gates, we were subjected to a random inspection. They found marijuana on the vehicle and we were both detained for around two hours in secondary inspection. He admitted that the marijuana was his and we were set free, with neither of us receiving any fines or penalties. According to my roommate, he was given a warning not to cross the drug again (it's legal in California, but not on federal property).
Cut to a week ago and my Sentri's been revoked. I need to write a letter to the Ombudsman, but I don't think I need to provide records since I was not convicted. I'm a straight arrow guy, so I don't know if I need anything besides the letter. Any suggestions?