Donaldson, who dramatically outed himself as a spy in December 2005, was gunned down at his remote hide-out near Glenties in Donegal just months later.
While the Real IRA later admitted responsibility for the murder, no one has ever been charged.
His family avoided Thursday's hearing, fearing that it would again be adjourned. They were right.
"[The Donaldson family] feel that the only mechanism whereby the truth might come out in relation to this is through the inquest proceedings or through [Police Ombudsman] Dr Maguire'sinvestigations now in the north," explained solicitor Ciaran Shields.
In 2002, prior to Donaldson confessing that he was an informer, he was arrested during 'Stormont-gate' - after police raids on Sinn Féin's offices during an investigation into an alleged spy-ring.
That brought down the power-sharing administration, but the charges were dropped in 2005.
However, Donaldson then went on camera to make the shocking admission that he had been a double agent after all.
"I have worked for British Intelligence and the RUC/PSNI Special Branch. Over that period, I was paid money," he said at the time.
I remember a senior Special Branch officer saying to me that every time we use an agent, we take a bit of their life, because once they cross that line, if they're found out there's usually an inevitable end to all of that - which is a body on the border, or a body somewhere.
His family had known nothing about the double life Donaldson had been leading and have long hoped the inquest into his murder would shed light on both his role and those of his MI5 handlers.
They are also desperate to know the truth about who carried out the killing.
"Why Denis Donaldson thought he could survive in Co Donegal, I don't know, because I think from the moment he revealed himself as an agent to use a term, he was a dead man walking," said Brian Rowan.
"He would've had enemies within mainstream republicanism, and of course for dissident republicans it would have been a big coup to claim the life of Denis Donaldson.
"I don't know if dissidents killed Denis Donaldson, I don't know if it was people who once would have been what he would have termed his comrades," he added.
Donaldson's handler, who called himself Lenny, phoned the double agent at his west Belfast home after he was warned by police that he was about to be exposed as an informer.
'Lenny' then kept in contact with him at his Donegal hideaway, but the handler has never been questioned by gardaí.
I don't think the full story of Denis Donaldson will ever emerge, and I don't think the full story of agent handling will emerge.
"The truth is too ugly [...] and those sorts of truths will be buried somewhere they will never be found," explained Brian.
Donaldson's death is to be investigated, but the coroner also wants the political, security and intelligence background leading up to the killing to be probed.
"It was running in the media in the aftermath of the murder that the cottage was under electronic surveillance, that's a matter that the family have raised with An Garda Síochána, and that Special Branch were well aware of the existence of the cottage," explained Mr Shields.
"It was searched during the course of the initial Stormontgate raid and also because members of the family have maintained that Special Branch continued intermittent contact with their father when he was in hiding in Donegal."
Gardaí are investigating the murder, and in Northern Ireland the Police Ombudsman is also re-examining the case. But the Donaldson family fear the inquiries could throw up more questions than they do answers.