frustrating investigation. rick was close to the answers he promised erica's grandmother. >> reporter: what kept you going during those times you felt you were hitting dead ends? >> a 2-year-old baby, erica hughes. >> reporter: the detective was ready to bring them in for tough questioning. rick had enough to arrest him, but wasn't ready, yet. he wanted more. both men from the walgreen's video to play them off each other in dualing interrogations. now, he had them. you have been waiting and waiting patiently. it's time to do your thing, right? >> the detective moves to get each suspect to implicate the other, not knowing he was nearly out of time. coming up -- >> reporter: you didn't know you were playing with the clock? >> no. no idea. >> when "dateline" continues. lasts through heat. through sweat.