I've been following since the beginning, this is the first thought I have to contribute.
I've been thinking about what the Chief is saying while showing the video. He's saying he is interested in the "third" guy, the "first" guy who walks by the children. Then he says we know who the children are and the second guy.
Okay so, I think he refers to the first guy to walk past the kids as the third guy could be because he is following the line of thought that PS is suspect person one, the second guy in video is the second suspect and now the first person in the video is the "third" suspect or someone he really wants to identify. This still leaves Ms QJ as possibly involved or she connects with PS shortly after the timeframe this crime occurs. I think this goes toward a theory that Cupcake has been moved around.
All just MOO