a camera was rolling as prosecutor fran humphries began his case. >> so this is purely motive evidenceablishes a motive for richard gagnon to end the lives of these two people. >> reporter: as humphries recalls, the case against rick was always motivation strong, evidence weak. not much more than a drop of charlie parker's blood on a shoe when i came right down to it. even so, humphries told the court the blood put rick at the murder scene. >> reporter: but he had a story for it, didn't he? >> he did. it didn't -- it didn't hold water. but it -- he had a story about it. >> reporter: humphries recited rick's version of how blood got on his shoe. he had gone into the parker house to get a set of car keys, sometime after crime scene techs had finished up. >> he looked to his right, which was the window leading in to the bathroom where big charlie had died and noticed the blood. >> reporter: rick said he worried bambi, pacing outside, might look in the window and freak out all over again. >> he went in and stepped through the bathroom and closed the blind. >> reporter: "and whoops, i stepp