liana hege: this poison in his car.ter that says, my brother did it? and they said, no, it's important. we got to look in your brother's car. you've got to convince him to let us-- you know, if you can talk to him, let him know. because if he leaves the station, this isn't going to be good. andrea canning (voiceover): adam eventually gave investigators permission, and they went outside to the parking lot. andrea canning: the moment of truth-- you open the vehicle door, and what do you find inside? they go out there, and they search the vehicle right where it says it's going to be in the letter. and we pull out a cardboard sleeve with the colchicine inside the sleeve. andrea canning (voiceover): and just like that, the investigators seemed to have the weapon right in his hand. that's your big moment in this case? big, big moment. andrea canning (voiceover): coming up, adam yoder, secret killer? it was frustrating. it just wasn't fitting. andrea canning (voiceover): this deadly puzzle wasn't solved yet. when "dateline" co