To freak her and everybody else out and once they are on to him to put fear into them.
Jesus Christ.. that was some hell of an episode, the best of the season so far. I had an inkling as to the reveal about halfway through the episode and a few minutes later they got it too.
3XK episodes turned out be amongst the best of the show and this one may have been the best yet introducing an equally creepy accomplice without ever actually showing him.
I loved all the reactions from the crew.. Lanie's mortal fear, Espo's rage and the absolute shock (or even fear) in Beckett's eyes when they heard the song at the end of the episode. I don't know if i ever saw her like this in Castle and it was chilling to see
Damn.. even thinking about it gives me the shivers
Yes, definitely the best episode this season so far and very highly ranked in the overall show, at least on my meter.