A new inquiry into the Claudy bombing appears to have been ruled out by the PSNI.
Nine people died - including an eight-year-old girl - and more than 30 were injured when three no-warning bombs went off in the County Derry village on July 31, 1972.
It has now emerged that, at the end of January, PSNI Assistant Chief Constable Drew Harris - along with other senior detectives - met with relatives of those who died to tell them that all available investigative options had been exhausted.
A PSNI statement said: “The investigation remains open but all available investigative options and actions have been exhausted. Should new information or evidence be forthcoming, police would progress this.
“Police would continue to appeal to anyone with information about the Claudy bombing to come forward so that the people responsible for this atrocity are brought to justice.”
A relative of one of those killed in the blast says that, despite the latest setback, the quest for the truth will continue.
The relative, who asked not to be named, said: “I’ll certainly not be giving up.
“Again, the police are suggesting that they’ve exhausted all avenues of investigation.
“I don’t for one minute believe this.
“Some people might be thinking that, if we stop talking about it, then we might just go away. Not for a minute.
“This atrocity may have happened more than forty years ago but, for me, it’s like yesterday and I live with the pain every day.
“I, for one, will never stop campaigning for the full truth to be revealed. I hope there are others out there that remain as determined as me.”
In 2010, a Northern Ireland Police Ombudsman’s report said detectives had concluded that Catholic priest, the late Father James Chesney, who was later moved to the Republic of Ireland, was a suspect.
It said the police, the state and the Catholic Church had covered up Fr Chesney’s suspected role in the bombing.
In his conclusions, the then Police Ombudsman Al Hutchinson said that, by ignoring opportunities to pursue Fr Chesney, the police had compromised the investigation.
That decision, Mr Hutchinson said, “failed those who were murdered, injured and bereaved”.