Police have defended their failure to realise in 1991 that Trevor Buchanan and Lesley Howell were murdered.
Detectives will be quizzed by Northern Ireland Police Ombudsman Al Hutchinson about why the deaths were believed to be suicides until dentist Colin Howell confessed in January 2009.
Detective Superintendent Raymond Murray said hindsight was always crystal-clear but regretted the delay.
"1991 was a very different place in Northern Ireland. There were 102 terrorist murders alone and CID (Criminal Investigation Department) were a lot more stretched than they are at the minute. They did not have so many assets available to them than they would have now," he said.
"However, the family have made a complaint to the Police Ombudsman and I completely understand that and I look to the Ombudsman now to investigate it and come back to us. If there are lessons to be learned, we will learn them.
"Things have moved on a great deal in 20 years and we regret they had to wait 20 years."
He said the murders were calculated and premeditated, made particularly chilling by the proximity of their children. The detective added they were: "Two young people with their whole lives ahead of them whose lives were cut short in a very calculated, cold and brutal murder.
"The thing that really strikes me about the last three to four weeks in court is I don't think anybody who sat in court, be it all the way through it or partially, could have missed the sheer emotional wreckage that this has left behind across all those families, across all those very many people.
"I don't think they have really felt such tension and emotion in a court as on the deliverance of the verdict and it shows how deeply this has scarred absolutely everybody that is involved in this."
He has spoken to both sets of families and said they had been reconciled. "It is very humbling and I have to say it has been a privilege to know and work with them, most closely probably the Buchanan family."