Lawyers for two journalists are claiming victory after judges indicated they would quash police warrants to search their homes and office.
Authorisation for the searches that led to the arrests of Trevor Birney and Barry McCaffrey were inappropriate, senior judges said.
A further High Court hearing will determine whether documents seized in the operation should be returned.
They relate to a police investigation into the murder of six men in 1994.
Mr Birney and Mr McCaffrey produced a documentary about the killings of Catholic men in a bar in Loughinisland in County Down.
Gunmen from the loyalist paramilitary group, the Ulster Volunteer Force (UVF), opened fire in the village pub as their victims watched a World Cup football match.
After a two-day hearing, Lord Chief Justice Sir Declan Morgan said: "We are minded to quash the warrants on the basis that they were inappropriate, whatever the other arguments."
Mr Birney said the decision is "a huge relief".
He told BBC News NI: "It's not very easy to explain what the last eight or nine months have been like for myself and Barry, and our families, friends and colleagues.
"I want to thank everyone who gave us support - we've had tremendous support from home and abroad, from people we've never met before, to people very close to us."
Solicitor John Finucane, who was acting on behalf of Mr McCaffrey, added: "This is a tremendous news day for my client and for Trevor Birney, and for all journalists.
"This will be a very important judgement for the freedom of expression, for the freedom of journalists to do their job."
Sinn Féin councillor Mr Finucane was installed as Belfast Lord Mayor last Tuesday.
The award-winning investigative journalists were involved in the documentary film, No Stone Unturned, which examined the Royal Ulster Constabulary's (RUC) handling of the Loughinisland atrocity.
They were detained in August last year, questioned and later released during an operation undertaken by detectives from Durham Constabulary, supported by Police Service of Northern Ireland (PSNI) officers.
Judicial review proceedings were brought in a bid to have the warrants declared unlawful.
All of the seized material remains sealed, with police having given an undertaking not to examine any of the documents and computer equipment pending the outcome of the legal action.