The State Coroner has demanded the removal of Detective Chief Inspector Pam Young from the investigation into the 1988 cliff-fall death of Scott Johnson after a television interview in which she gave weight to the suicide theory over murder.

Coroner Michael Barnes believes DCI Young's "unprecedented" interview on the ABC's Lateline -  on the same day he ordered a third inquest into the death last week – undermines public confidence in her impartiality and he will be advised whether it amounted to contempt.

The family of Mr Johnson believes the 27-year-old mathematics prodigy was thrown to his death from North Head among a spate of gay-hate murders in Sydney in the 1980s, but DCI Young's 445-page report to the coroner advises against that possibility.

In her interview, the Unsolved Homicide Team investigator accused former police minister Mike Gallacher of improperly "kowtowing" to the demands of the victim's brother Steve Johnson. He has spent about $1 million on his own investigations, which led a second coroner to overturn the original suicide ruling and make an open finding in 2012.

DCI Young told Lateline she had given the coroner "extra information" supporting the suicide theory and cited the "consistent" recollection of Mr Johnson's long-term partner, Michael Noone, that Scott had confessed to wanting to jump from the Golden Gate Bridge four or five years earlier – when he had mistaken fears about AIDS following a casual sexual encounter.

In a 2013 interview included in the Young report, Mr Noone, who had struggled to believe the original suicide finding, says it is possible that Scott, remorseful over a recent infidelity, could have jumped to his death or that he simply fell. But Mr Noone also says it is unlikely that Scott – whose naked body was found at the base of the cliff near Blue Fish Point – would have walked around alone and nude at the gay beat. It was a "real possibility" that Scott  was lured there or met someone and "something happened".

The Johnson family asked for DCI Young's removal immediately after the Lateline interview and a week later, on Monday, their counsel received a copy of a letter from the Crown Solicitor's office to the NSW Police Force asking for the investigator's removal.

The letter from senior crown solicitor Naomi Malhotra to police force general counsel Clair Hodge says: "The State Coroner is concerned that your characterisation of the conduct that precipitated this correspondence as not as circumspect as the approach usually taken by the NSWPF unduly diminishes the seriousness of what has occurred.

"When the Officer in Charge of the investigation speculated on national television about the weight to be given to key evidence she knew would come before the inquest and in effect queried whether the investigation she had undertaken was even appropriate, she engaged in a departure from the usual standards of conduct in such matters that is unprecedented in the State Coroner's experience.

"It clearly has the potential to undermine public confidence in the impartiality of DCI Young's investigation and her commitment to it."

The senior crown solicitor was yet to advise whether DCI Young's interview "amounts to contempt or would otherwise undermine the integrity of the hearing".

"In any event, the State Coroner considers the continued involvement of DCI Young will make it very difficult to regain the confidence of the key stakeholders in the inquest and may have a tendency to detract from the real issues, namely the determination of the manner and cause of Scott Johnson's death.

"The State Coroner acknowledges that DCI Young has an intimate knowledge of a very complex investigation and that she has devoted an enormous amount of time and effort to it."

Her report would be tendered to the inquest and "she is likely to be called upon to give evidence".

But Mr Barnes wanted a new investigator to be appointed to perform any further inquiries that "might be necessary" and asked that this officer be answerable to the head of the homicide squad, Detective Superintendent Mick Willing, "and not DCI Young".

Superintendent Willing conceded last Tuesday that some of DCI Young's remarks had been "inopportune".

During her Lateline interview, DCI Young admitted her relationship with the Johnson family had broken down and that this "is a point of sorrow for me", but she suggested it was because she had resisted the influence of Steve Johnson.

She said it was wrong of the then minister, Mr Gallacher, to give priority to one case over hundreds of other unsolved cases in which families wanted answers.

It is understood DCI Young and her police colleagues felt ambushed when the minister called her into a meeting with the Johnsons and sought action on the case. They thought it improper for him to intervene with operational police.

Mr Gallacher rejects the claims and says he merely attempted to help family who has been waiting 26 years for answers.

Fairfax Media has sought a response from DCI Young or Superintendent Willing and received the following response: "NSW Police has received correspondence from the Coroner and will respond to him in a timely and appropriate manner."

In her ABC interview, DCI Young stressed that Scott Johnson had talked about "committing suicide from a height over water" in the case of the Golden Gate Bridge.

"Lo and behold, in 1988, his body is found at a height of 60 metres from a cliff over water."

Steve Johnson told Fairfax Media on Tuesday the family was encouraged by the State Coroner's action.

"We will rely heavily on information from the public, so trust needs to be immediately restored.  We are looking forward to working with whomever the NSW Police put on the investigation - we're solely focused on discovering the truth about how Scott died and appealing to people to come forward with information that can help us in this quest."