Julie Mugford held up the investigation big time. If she had told the truth straightaway, a lot of the evidence wouldn't have been destroyed, and Colin wouldn't have thought his ex-wife was a murderer for so long. Any normal person would have recoiled in horror if their partner told them they had just hired someone to kill five people, including two children, but she did not do that - she covered up for him for a month, carried on seeing him, and even going away with him.