The Government has been accused of frustrating the release of files that expose a "state sponsored programme of assassination" in Northern Ireland.
A lawyer for the family of a Belfast father-of-three shot dead by loyalist paramilitaries during the Troubles made the explosive claim during a coroner's court hearing ahead of a new inquest into the death.
Gerard Slane, 27, was shot dead by the Ulster Defence Association (UDA) at his home at Waterville Street, west Belfast in 1988.
Barrister Fiona Doherty said the extent of collusion between paramilitaries and the security forces in the murder was "as bad as it gets" as she demanded an explanation for delays in disclosing police and military files to the inquest.
"This was a state sponsored assassination programme going on here of which Gerard Slane was an entirely innocent victim," she told coroner Suzanne Anderson at a preliminary hearing in Belfast Coroner's Court.
Ms Doherty was responding to the revelation that it will likely take at least six more months before sensitive Police Service of Northern Ireland (PSNI) and Ministry of Defence files are handed over to the coroner.
Collusion between loyalists and rogue elements of the security forces has been detailed in a series of official investigations in the years since the Troubles ended.
Separate probes by former Met police commissioner Lord John Stevens, retired Canadian judge Peter Cory, and most recently QC Sir Desmond de Silva have all examined allegations of state involvement in murders committed during the Troubles
Particular focus was placed on the de Silva report at today's hearing in Belfast.
in 2011 Prime Minister David Cameron commissioned Sir Desmond to assess claims of collusion in the murder of Belfast solicitor Pat Finucane by loyalists in 1989. His probe also examined Mr Slane's killing.
Notorious state agent Brian Nelson, a UDA man working for British intelligence who died in 2003, is understood to have been involved in planning the deaths of both Mr Slane and Mr Finucane.
Ms Doherty asked why Sir Desmond had been able to obtain all the information he needed from the state to compile his report within a year, yet the coroner was still waiting for the same material over three years since the inquest was ordered by Northern Ireland Attorney General John Larkin.
"He (Sir Desmond) was able to be provided with all the material he saw as relevant not just in regard to the murder of Pat Finucane but also the murder of Gerard Slane and the structures and system that facilitated both those murders," she said.
"He was provided with all that material and was able to produce a comprehensive two volume report by December 2012 - that was two years ago."
She added: "Two years after he reported we have got a fraction of that material and we don't know when we will get the rest."
The barrister was heavily critical of written responses to requests from the coroner from both Northern Ireland Secretary Theresa Villiers and the Cabinet Office. The letters suggested they may hold relevant material but asked for further information from Ms Anderson.
The court heard that a reply has not been received to a similar letter sent to the Public Prosecution Service in Northern Ireland.
"You know Madame coroner, the dogs on the street know, it is publicly known that Sir Desmond de Silva's report contained information about Gerard Slane," said Ms Doherty.
"What is going on here? Why are people not answering letters? Why are people questioning the fact they hold relevant material?"
She added: "This court is being treated with something akin to contempt."
In regard to the lack of reply from the PPS, Ms Doherty said: "If nothing else that is the height of discourtesy."
She said a representative from the NIO should come to court to explain the delays.
Barrister Mark Robinson, representing the PSNI and MoD, explained the Cory and de Silva reports were based on vast volumes of material.
He asked for more details on specific material requested to help expedite the disclosure process.
The lawyer said it was vital that all documents were rigorously security checked before being handed to the coroner. He also noted the volume of work currently facing the authorities in terms of other legacy inquests.
"The process is being engaged in," he said.
"But we must ensure what goes out is safe. That takes time, it takes careful analysis of documents and it must be viewed in the context of the number of these inquests and the pressures upon those performing the exercise.
"These matters are being expedited as fast as they can be in the circumstances."
Ms Anderson asked Ms Doherty to outline her concerns in a written submission and said she would forward those on to the relevant authorities for response.