Tribute: [s11e19]

: Prentiss enlists the BAU's help because the case is personal; the killer murdered a Scotland Yard operative, Louise Hulland, whom Prentiss had mentored and sent undercover.

: Prentiss initially suggests that the team look into diplomats to explain how the killer has been able to travel so easily between the UK, Russia, and the United States. [S11E19] Tribute

: The episode also focuses on the team's "paperwork" and emotional processing following the recent departure of Derek Morgan . "Criminal Minds" Tribute (TV Episode 2016) - IMDb : Prentiss enlists the BAU's help because the

: The episode's title refers to the UnSub, Michael Lee Peterson, who pays "tribute" to famous serial killers by meticulously copying their methods, such as Jack the Ripper , the Boston Strangler , and Son of Sam . "Criminal Minds" Tribute (TV Episode 2016) - IMDb