The mother of a young man killed in Broome is outraged his attacker has had his murder charge dropped after police interviews were deemed inadmissible.
Joshua Timothy Warneke, 21, was walking home from a night out drinking with his friends in Broome on February 26, 2010 when he was assaulted on Old Broome Road, sustaining fatal head injuries.
Gene Gibson was charged with his muder but pleaded guilty to the lesser charge of manslaughter on Friday, just weeks before he was due to face trial.
The plea was accepted by State prosecutors after Justice Stephen Hall threw out interviews in which Gibson allegedly admitted running over the 21-year-old and hitting him with a rock.
Police alleged Mr Warneke was killed with a metal pole.
Justice Hall found the officers involved in the two-year investigation had committed a string of "serious breaches" of the Criminal Investigation Act that cast significant doubt on the reliability of the evidence.
He ruled police interviews held over two days after major crime squad officers arrived at the remote Kiwirrkurra Community in August 2012 were not voluntary and it would be unfair to allow them to be admitted in evidence.
The judgment found police failed to caution Gibson on his right to silence at an initial unrecorded interview and the 21-year-old had not understood the caution given by officers when they belatedly began recording.
Justice Hall said there was no reasonable excuse for a decision not to get an interpreter for Gibson, who was at a "serious disadvantage" because he had only a basic level of English.
The victim's mother, Ingrid Bishop, has today slammed the “incompetent” police investigation and called for an independent review of the case.
Ms Bishop said the fact Gibson would be punished for manslaughter was “an absolute joke”.
“The process ... has been a debacle,” Ms Bishop said.
“I'm disgusted and appalled.
“It's a very, very sad day for the judicial system here in WA.
“I just hope this issue isn't swept aside. The family certainly isn't going to allow it to be swept aside.
“I'm expecting there will be a review of this process ... that will be conducted by an independent body.
“We need to rip this process apart and find out what on earth went wrong.”
WA Police Commissioner Karl O'Callaghan later said there would be a full internal investigation into the conduct of the investigating officers.
"All internal investigations of this type are also subject to independent oversight by the Corruption and Crime Commission," a spokeswoman for the Commissioner said.
Criminal Lawyers' Association of WA vice-president Philip Urquhart said it was bewildering that experienced police officers had failed to follow basic rights clearly spelt out in legislation since the 1990s.
"It might be time for the Police Commissioner to have some refresher courses for his officers in how to conduct interviews," Mr Urquhart said.
Gibson will be sentenced on August 21.