When the team arrives to investigate the scene of the Son of Sam copycat murder, there is a postal vehicle driving by the opening of the alleyway. David Berkowitz, the Son of Sam killer, was working for the U.S. Postal Service at the time of his arrest.
Paget Brewster reprises her role as Emily Prentiss for the second time since leaving after season 7, the first being in 200 (2014). She originally wanted to fill in for A.J. Cook during her maternity leave earlier this season, but the scheduling conflicted with the show that she was filming, Grandfathered (2015).
Nobody has ever been charged with the Boston Strangler murders.
Unusually for serial killers, the Boston Strangler's victim's ages ranged greatly, from 19 - 85 years old.
Albert DeSalvo was responsible for 2 separate sprees of sexual assaults, under 2 different monikers. The first as the "Measuring Man", a name he was given for claiming to be from an agency looking for models and groping women under the pretense of taking their measurements. For which he served 11 months of an 18 month sentence.
Shortly after his release from prison DeSalvo turned to rape, which earned him the name "Green Man" for the green boiler suit he wore to impersonate a workman. DeSalvo received a life sentence for the series of attacks.