The Sunday World reporter was shot dead by the LVF as he walked home with his wife from a pub in Lurgan on September 28 2001.
He was the first working journalist to be killed here since the start of the Troubles in 1969.
Ahead of the 24th anniversary on Sunday, Amnesty International called for a fresh investigation into the murder.
It also wants a long-awaited report by a watchdog to be released.
Martin O’Hagan
In September 2013, the Director of Public Prosecutions called in the Police Ombudsman to investigate the police handling of the case.
Amnesty said the ombudsman has confirmed the report is complete, but it is “not in a position to provide specific timeframes” for its publication.
Patrick Corrigan, Amnesty International’s Northern Ireland director, said: “The murder of Martin O’Hagan casts a long, dark shadow over press freedom in Northern Ireland.
“The public execution of Martin O’Hagan was designed to send a clear message to journalists in Northern Ireland that they are not safe.
“It is simply unacceptable that, in the 24 years since Martin O’Hagan was shot dead, no-one has been held accountable.
“This failure by the state has created an environment of impunity for those who continue to make deaths to journalists in Northern Ireland today.
“It is now 12 years since the Police Ombudsman was called in to investigate the police handling of this case. We urge the Police Ombudsman to publish without further delay the report of their investigation.
“We need a fresh investigation into the killing itself – one that will end the impunity enjoyed for 24 years by Martin O’Hagan’s killers.”
Martin O’Hagan was shot dead by the LVF in 2001
News Catch Up – Friday 26th September
Séamus Dooley, NUJ assistant general secretary, said there was an unwillingness to treat Mr O’Hagan’s murder “with the necessary degree of seriousness”.
“To mark another anniversary of Martin O’Hagan’s brutal killing with yet no progress on an independent investigation into his killing is shameful, and sends a deeply concerning message about the UK and Irish governments’ failure to tackle the impunity enjoyed by those who target journalists,” he said.
Mr Dooley added: ”It is time for all political leaders in Northern Ireland to end the game of ‘pass the parcel’ and finally deal with this issue as a matter of urgency.”