GAY killer Allan Grimson may have killed up to a dozen people.
Police fear the twisted sailor could have acted out a murderous ritual after being spurned by missing teenage naval rating Simon Parkes.
They believe the former Portsmouth petty officer murdered Mr Parkes on December 12 1986, and then could have struck 11 more times – each time on December 12 – before he was caught.
Grimson was jailed for life for two murders, which happened on December 12 1997 and the same date in 1998.
Police are investigating if Grimson killed on that date every year.
A BBC documentary, Bodyhunt: The Search for Simon Parkes, revealed that two witnesses placed Grimson and Mr Parkes in the same pub on the night Mr Parkes went missing.
But a search has failed to turn up a body and Grimson has repeatedly denied being involved in his disappearance.