They never denied that it was real:
https://www.theguardian.com/science/2016/aug/18/fake-human-sacrifice-filmed-at-cern-with-pranking-scientists-suspected
“These scenes were filmed on our premises but without official permission or knowledge,” a Cern spokeswoman told Agence France-Presse in an email.
“Cern does not condone this type of spoof, which can give rise to misunderstandings about the scientific nature of our work.”
The “investigation” under way was an “internal matter”, she said.