John Stalker was an old school detective greatly admired by colleagues, feared by criminals and respected by the public as a dedicated police officer.
Born in Manchester, his career began in the city on the beat as a young cadet but he quickly rose through the ranks, working in CID for 16 years to become a Detective Superintendent.
As a junior detective one of his roles included involvement in the notorious Moors Murders of the 1960s.
His job included developing the photographs and listening to the tape recording made by Ian Brady and Myra Hindley as three-year-old Lesley Ann Downey was sexually tortured and murdered.
The tape was recorded at the house in Wardle Brook Avenue, Hattersley, as Lesley Ann pleaded with them "Please God, help me" and "Don't undress me, will you?"
Her cries reduced the judge, jury, courtroom spectators and even hardened police officers to tears.
Mr Stalker, who was then a detective sergeant, expressed the feelings of many in the courtroom when he said: "Nothing in criminal behaviour before or since has penetrated my heart with quite the same paralysing intensity."
He also held posts within the Serious Crime Squad and the Bomb Squad and became head of the first drugs squad at Greater Manchester Police (GMP), where he served most of his career.
In 1978 - aged 38 - he was appointed head of Warwickshire CID, the youngest Detective Chief Superintendent in the country - later becoming Deputy Chief Constable of the Greater Manchester Police in 1984, the biggest police force outside London.
He travelled the world studying terrorism and crime in Europe, the USA and South America which led to his appointment to head an inquiry into policing in Northern Ireland.
A policeman investigating other policemen, he was met with some opposition from inside the shadowy world of state security at war with paramilitaries in the troubled country.
Mr Stalker was asked to investigate the RUC shootings of six people but was removed from the inquiry shortly before it was due to report in 1986.
There was also behind-the-scenes fears that a Masonic plot within the police against Mr Stalker could be revealed during one of the most controversial episodes of the Troubles, according to newly declassified files that were released in 2016.
He was taken off the case at the moment he believed he was about to obtain an MI5 tape of one of the shootings.
Suspended over allegations of associating with criminals, he was later cleared of any wrongdoing and reinstated to his job as deputy chief constable of Greater Manchester Police but his report was never published.
The high-profile and highly controversial inquiry saw him regularly in the national spotlight.
He was just as often in the public spotlight after his retirement from the police in 1987 as he was while still a serving officer; carving out a career in the media as an expert on policing, appearing on crime-related TV shows including Crimestalker and writing his autobiography.
He married his wife Stella in 1961, the couple settling in Lymm, Cheshire, where he lived until his death, aged 79.
He is survived by his two daughters, six grandchildren and two great-grandchildren.