High-profile NSW homicide detective Gary Jubelin, who worked the Bowraville murders and Matthew Leveson's disappearance, has quit the force just months after being sidelined from the William Tyrrell case.

Key points: In March, it was revealed the detective was being investigated over allegations he used his mobile phone to record someone without a warrant

In March, it was revealed the detective was being investigated over allegations he used his mobile phone to record someone without a warrant It's understood Mr Jubelin has co-operated with the Professional Standards probe

It's understood Mr Jubelin has co-operated with the Professional Standards probe President of victims' group Support After Murder, Peter Rolfe, said he was horrified by news of the Mr Jubelin's departure

The ABC understands the veteran detective will retire on his own terms, instead of waiting for the outcome of an internal probe into misconduct allegations.

Detective Chief Inspector Jubelin, who joined NSW Police in 1985, confirmed he was leaving the force but said he could not comment further.

In March, it was revealed the detective was being investigated over allegations he used his mobile phone to record someone without a warrant, and staff management complaints — accusations he has strongly denied.

At the time, the Head of NSW Crime Command, Acting Assistant Commissioner Stuart Smith, said they could not have an allegation of misconduct and not deal with it.

It is understood Mr Jubelin has cooperated with the Professional Standards probe, which saw him confined to desk duties, but that the investigation had taken a toll.

The president of victims' group Support After Murder, Peter Rolfe, said he was horrified by news of Mr Jubelin's departure.

NSW Homicide Commander Mick Willing (left) and Detective Inspector Gary Jubelin in Macksville. ( ABC: Fiona Poole )

"This is an abomination," Mr Rolfe said.

"Gary is not only brilliant; he is one of the most compassionate cops I have ever had the privilege of meeting."

Mr Rolfe has supported homicide victims' families since his partner was murdered in 1994 and said some families were in tears over Mr Jubelin's retirement.

"Gary is one of the rare type of cops who show an interest in families," Mr Rolfe said.

"He is a unique sort of person and he will be sadly missed by victims' families and members of the NSW police."

Mr Jubelin has worked several high-profile cases and led the search for William Tyrrell, who disappeared from his grandmother's home on the NSW mid-north coast in 2014.

At first, investigators thought three-year-old William had wandered off and got lost, but police later said they believed he was abducted.

William Tyrrell has not been seen since September 2014. ( AAP: NSW Police )

Since William went missing, police have identified almost 700 people of interest, conducted hundreds of interviews and gathered more than 4,000 pieces of evidence.

On the second anniversary of his 2014 disappearance, NSW Police announced an unprecedented $1 million reward for information leading to William's recovery.

A five-day coronial inquest into his disappearance earlier this year focused on William's biological parents and the events on the day he went missing.

The inquest will re-open in August.

Mr Jubelin also led investigations into the death of Sydney woman Courtney Topic and the stabbing murder of Michelle Leng.

He received a standing ovation from the victims' families during a parliamentary committee when speaking of racial discrimination during the Bowraville case.