WA police have win in Evil 8 case

WA police has avoided the humiliation of having key evidence including a confession thrown out in one of the state's highest profile cases after a major bungle by two WA detectives investigating the Evil 8 paedophile group.

The detectives admitted in the District Court to breaching WA's criminal act when they kept Alfred John Impicciatore, 46, detained beyond the six-hour limit after arresting him on May 14, 2015.

Detective Natalie Wynen was not finished interviewing him and so organised for her manager, Senior Detective John McTernan, who helped arrest Impicciatore, to authorise an extension.

However WA's Criminal Investigation Act demands that only an "independent" senior police officer - who is not involved in the investigation - can sign off on extending an arrest.

Impicciatore was charged that day on various counts including sexually penetrating a child in March 2015 and has since pleaded not guilty.

His lawyer Mara Barone said it was a serious and reckless abuse of powers by police officers who were desperate for a confession because they lacked evidence to charge him.

Det Sgt McTernan said it was an oversight and he had forgotten that law and Det Wynen said she was not even aware of it.

District Court Judge Vicki Stewart ruled the "desirability" and importance of the video interview as evidence in the case outweighed the "undesirability" of allowing it due to the police's mistake.

The fact that the extension was less than half an hour beyond the six hours was relevant, Justice Stewart said, and while she agreed with Ms Barone that the breach was serious she believed it to be an honest mistake by the detectives.

The other men in the case charged with abusing and drugging the girl, aged 11 to 13 at the time, include her own father who had pimped her out and five other men who are now serving prison terms.