Respectfully, BBM - Maybe the medicine KB went to Walmart to get PF was something PF thought would work to his advantage if the receipt was found by LE or family, etc. that it would help play into his story of KB taking off on her own and make it appear as if she had the stomach issues, and not him. But then again, I'm not sure his brain could've thought that far ahead but one never knows. I think he was trying very hard to make it look as if she just up and took off and that he would never be implicated in any way regarding her disappearance. If he was only half as smart as he thought he was........
And another thing, I doubt he just started having stomach issues that night. IF he had any stomach issues, I would venture to say it had been for a longer time period than just that 1 night and so therefore, he would've had medicine on hand for it, especially with having an RN in the same household. So, I'm not buying any of his BS about his stomach issue problem(s).