8On the evening of August 21,1983, Metropolitan Police detectives raced to the cells of London's Clapham Police Station to find a prisoner dead and his cellmate sat cross-legged and quiet in the corner.

Kieran Kelly, a laborer from Ireland, quickly confessed to strangling the prisoner - and then stunned officers by confessing to dozens of unreported and unsolved murders over the previous 30 years.

Detectives believed they were in the presence of Britain's most prolific serial killer yet Kelly was convicted on just two of his admissions and his story went unnoticed until 2015, when a former police officer who worked on the case claimed the killer's crimes were covered up by the British Government.

Strangulations, murders on the London Underground, an internal Metropolitan Police review - as the story's elements whipped the international news media into a frenzy, journalist Robert Mulhern set off on a methodical search for the truth against the backdrop of an ever-increasing body count.

Could Kieran Kelly really have murdered 31 times?