When the unsub transports his victims to the kill room, he is whistling the song "Johanna" from the Stephen Sondheim musical Sweeney Todd: The Demon Barber of Fleet Street a musical about a serial killer. The words of the sequence he is whistling are:
I'll steal you, Johanna,
I'll steal you.
Do they think that walls can hide you?
Even now I'm at your window
I am in the dark beside you, Johanna.