The movie Rick and Alexis are watching as the episode commences is Night of the Living Dead.
After Castle, Beckett, and Ryan watch the footage from the murder, Castle turns around and says "they're here" in front of the static-filled screen. This is a clear nod to Heather O'Rourke's famous line from Poltergeist (1982).
Actor Fredrick Lehne (Addison Smith) had previously worked with Nathan Fillion on Firefly (Heart of Gold).
The victim asked someone to take pictures of the place he ended up being killed. This is similar to Johanna Beckett having taken pictures of the alley she ended up being killed in.
Amanda Walsh (Lulu, Jack's producer), Vernee Watson (Mercy LaGrande / Mercedes King), and Mark Harelik (Pete Benton) have all appeared on The Big Bang Theory.
Josh Hopkins: (from Cougar Town (2009)) makes an uncredited appearance as a station house police officer who hands a file to Jon Huertas. The cameo happens in the first 10 minutes of the show.