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
The overnight forecast for the Calendar region from Jon Mitchell.
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A man who caused a multi-vehicle collision by using his phone behind the wheel of a lorry has been jailed.