The three officers face possible demotion after their arrest and questioning of the 29-year-old with intellectual limitations was criticised by a NSW judge, public prosecutors and the state's police watchdog.
Despite being told by the man's lawyer that he did not want to be questioned, police interviewed him twice - including after he indicated five times that he wanted to stop to seek legal advice.
One constable was also found to have recklessly put false information to the suspect.
Another officer "did less than the bare minimum" in his role as the police station's custody manager, having been told by a lawyer the suspect did not want to be interviewed, the Law Enforcement Conduct Commission said.
One constable was found to have recklessly put false information to a suspect. (Candice Marshall/AAP PHOTOS)
The man admitted to several matters including things he could not have been involved in, the watchdog said.
Subsequent charges were tossed out two years later by a judge due to the pressure placed on the man.
The watchdog's report on the case follows its December 2023 finding that NSW Police Force had a systemic problem of officers interviewing vulnerable people after they had received legal advice and said they did not wish to be interviewed.
In some instances, pressure and a perceived obligation to make a prosecution stick meant officers pushed a case in any way that allowed a charge to be laid, a criminal lawyer said.
"It's the hope that they will get away with it," Redfern Legal Centre supervising solicitor Samantha Lee told AAP.
"It not only has terrible impacts for the person in the police station being questioned but also as in this recent case, police are risking the whole criminal process.
"You've got the Miami Vice coming through in Sydney police."
She also highlighted what she described as tension between a custody manager's desire to be part of the police team and their obligation to ensure arrested people's rights are adhered to.
"What's showing up in these cases is there is a huge conflict of interest," Ms Lee said.
The charges were tossed out in 2022 when a judge found the man had clearly exercised his right to silence.
"Contravention of the accused's right to silence, particularly as a vulnerable person and in the absence of a support person, is very grave," Judge Siobhan Herbert said.
Public prosecutors then referred the matter to the police watchdog.
The commission, which made serious misconduct findings against all three officers, rejected claims by one officer that systemic issues mitigated his conduct.
"The inability of an officer to respect such a basic request cannot be blamed on any other factor," the commission said in a report.
"Regardless of systemic issues, any officer with common sense and basic respect for fairness would have complied with (the suspect's) request to stop the interview for legal advice."
The watchdog recommended disciplinary action such as reducing the officers' rank but not dismissal.
The force said it was considering the recommendations and noted changes since the 2020 incident.
"This includes instructions issued to officers in December 2023 regarding the process to follow when a person declines to be interviewed," a police spokeswoman said.
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