The Supreme Court is ruling on whether a convicted murderer who has been given parole can keep his identity secret from the press and public.
Details of his offending cannot be reported until the highest court in the land makes its decision.
Referred to as "C", the killer has been allowed back into the community on licence by the Parole Board and is in the process of changing his name as he starts a new life, the court was told at a hearing in October.
C's lawyers are challenging a Court of Appeal refusal to grant him anonymity, which was made while he was detained and receiving treatment for mental illness.
The case raises a point of general public importance - whether mental health patients are entitled to anonymity when involved in legal proceedings connected with their detention, care or treatment under the Mental Health Act.
The issue arose after C applied for judicial review of a decision, made well before he won parole, refusing him unescorted leave in the community.
The appeal court judges upheld a ruling by High Court judge Mr Justice Cranston that C - initially referred to as "X" - could be named during the review application.
Stephen Knafler QC, appearing for C, argued legal challenges involving mental health patients should be held in private - or at least with the individual's identity protected.
Mr Knafler accepted in the appeal court that C's criminal activity was "high up on the scale of horrific".
He told the justices that all mental health tribunals protected the identities of patients, and there was no reason why High Court and appeal court hearings should be any different.
He acknowledged the "fundamental common law principle" that court cases must be held in public, but argued mental health cases were "a protected class" and fell outside the general rule.
Mr Knafler said that if he was not right on that broad argument, the "exceptional" circumstances of C's case meant that he was entitled to anonymity in any event.
The QC told the justices - Lady Hale, Lord Clarke, Lord Carnwath, Lord Wilson and Lord Hughes - that the most intimate and private details about patients were revealed at legal challenges to decisions about their treatment.
Patients were "under an extreme level of compulsion" and had no real choice about those "extremely frank" details being disclosed to courts and tribunals.
If their identities were revealed, and the details of their case and treatment became public knowledge, without identity protection they could face a "media bombardment" and be put at physical risk, or risk of being shunned, and attempts to rehabilitate them could be impeded.
Mr Knafler said: "The courts below simply failed to bring the physical risks, and other risks, into the balance."
He said: "I am very conscious of the fact that many will consider C simply does not deserve this level of care and consideration."
Many would feel the application for anonymity was to ignore "the terrible, terrible pain he has caused and the great public interest in his case".
But if the court did not intervene, "everything said (about C) is liable to be published to the whole world and be on the internet for ever and a day".
Katherine Olley, appearing for the Justice Secretary, opposed the principle of mental health patients as a whole falling into a protected class entitled to anonymity, but said applications should be considered on a case-by-case basis.
Ms Olley submitted the power to grant anonymity could not be used "simply to protect privacy or avoid embarrassment".
The Media Lawyers Association told the court the case "raises significant issues about the open justice principle" and anonymity can only be justified "where it is strictly necessary".