When approached by Calendar, a spokesman said: "North Yorkshire Police invited the National Policing Improvement Agency to conduct a second voluntary review of the investigation in 2010.
"Their report concluded that the investigation had been conducted with integrity and objectivity and that, where individuals had been subject to investigation, no investigative opportunities had been overlooked.
"The reviewers noted that good practice was evident in the investigation and that those strategies reviewed conformed to nationally approved standards."
See the interview on Calendar tonight at 6pm.
More top news
Youth Fight for Jobs has organised demonstrations to coincide with the inauguration of America's 45th president
Valantis Barkas said there was "no evidence" Konstantinos Barkas had knocked the Sheffield toddler down and covered it up
Phase 2b of HS2 from the West Midlands to Leeds, South Yorkshire and the East Midlands, will begin operation in 2033.