The father of World's End murder victim Helen Scott said he was devastated by the judge's decision to throw out the case against Angus Sinclair.
Morain Scott said he had hoped the case would bring closure for him
Morain Scott, 77, said outside the High Court in Edinburgh, he was "absolutely shattered" after hopes of a conclusion 30 years on had been dashed.
He spoke of the effects of the murder on his family and said he was convinced Sinclair was involved in the killings.
The death of his teenage daughter had also killed his wife, he added.
Mr Scott said: "I am absolutely shattered, words can't explain how I feel.
"Thirty years of trying to get a conclusion... I promised I would stick by this and get justice which, honestly, I don't think I got today.
"At least had it gone to a jury, you can accept their decision, but for the case to be thrown out after all the hard work that was put in just astounds me completely."
Mr Scott said he thought there was enough evidence in the two weeks of prosecution case.
"The girls had to get to East Lothian somehow. Both had their hands tied and to think that any one person did that is unbelievable.
"It was proved in court that DNA from Helen's coat was Sinclair's. I am just gutted. Absolutely gutted."
The girls were last seen alive at the World's End pub
Asked if he thought Sinclair did it, Mr Scott replied: "Yes I do. He was involved. Whether as an accessory or not, he was involved."
"There had to be a vehicle. There had to be someone who knew the area, which he did.
"I don't know how, if the two girls were there, one person could have tied their hands behind their backs."
Mr Scott, 77, added: "I just want to be left in peace now to see the rest of my days out.
"I just want to think about Helen and Christine, who had their lives taken away from them just when they were starting out."
Mr Scott's son, Kevin, said both families had been left with feelings of "disappointment and emptiness" following the decision.
"Having given so much support over the past two years, since the charges were brought, it obviously comes as a bitter pill to swallow," he added.
"Having said that, we cannot thank enough Lothian and Borders Police for the tenacity and time that they have spent to try and bring a conclusion that would be acceptable to us as a family."