For some reason I missed this episode. Zanax (benzodiazipine) would have supressed the bodily responses the polygraph would measure. He also may have been on pain medication for his injury. Mixing a pain med (opiate) with methamphetine is very dangerous add a benzodiazipine like zanax would be deadly. I "feel" the stepmother was not happy that the trip was postponed. She may have been angry at Jeff because of the divorce. I would research her to the max. I think thats called motive?