A person confesses to murder but faces no criminal charge: this is the unusual territory into which the Matthew Leveson case appears to be venturing.
But so-called "immunities" from prosecution granted to the key suspect, Mr Leveson's former boyfriend Michael Atkins, need to be examined with care.
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The night Matthew Leveson went missing
Matthew Leveson's brother describes the last time he saw Matthew at a nightclub in Sydney in 2007. Vision: 60 Minutes, Channel Nine (November 2015).
Legal experts told Fairfax Media the precise terms of a deal with the NSW Attorney-General, which have not been made public, would require close analysis before it could be concluded Mr Atkins will never face prosecution for any offence.
Nevertheless, a prosecution would be extremely difficult for a number of reasons.
First, Deputy NSW Coroner Elaine Truscott granted Mr Atkins a certificate under section 61 of the Coroners Act which provides his evidence before the inquest cannot be used against him in court.
This extends to evidence obtained as a "direct or indirect" consequence of his evidence.
The certificate is not a blanket immunity from prosecution and it does not protect a person against a charge of perjury if they give untruthful evidence.
Mr Atkins admitted to lying at the inquest, leaving him open to a perjury charge.
This gave NSW Police a bargaining chip, and led Attorney-General Gabrielle Upton to grant Mr Atkins "conditional immunity" from a perjury charge in exchange for leading police to Mr Leveson's body.
That immunity, the second crucial factor in this case, is conditional on the body being found.
A senior criminal barrister said such a deal was "unheard of" and it was not clear it was in the public interest.
The third complicating factor is Mr Atkins was tried and acquitted in 2009 of Mr Leveson's murder or manslaughter.
This brings into play the "double jeopardy" principle, which provides a person cannot be tried more than once for the same crime.
There is an exception in cases where "fresh and compelling" evidence of guilt comes to light.
Forensic evidence from a body or crime scene might meet this definition, although it is unclear if this would be regarded as evidence covered by the section 61 certificate.
But other witnesses might come forward if a body was located.