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 force is issuing security warnings after 157 bicycles were taken last month
The four people who were all related were killed on the A64 near Malton as they returned from a wedding in Leeds.
Sarah Champion quit in June as 172 Labour MPs backed a vote of no confidence in the party leader - but she has now asked for her job back.