Police have marked the anniversary of a "Real IRA" murder in Derry by mounting a fresh appeal for information.
On Thursday the PSNI said it knew the identities of the bombers who killed a workman in the city last year, but still did not have enough evidence to bring a case to court.
Mr David Caldwell (51), a building worker, died at a Territorial Army base in the city on August 1st last year after a lunch-box he had handled exploded.
The dead man was the first victim of the dissident group since the Omagh bombing of August 15th, 1998, which claimed the lives of 29 people including a woman pregnant with twins.
He had been a member of the Ulster Defence Regiment during the 1980s, although this is not thought to have been a factor in the killing, which detectives believe was indiscriminate.
Eight suspects have been interrogated, five of them in the immediate aftermath of the bombing. But the PSNI admitted yesterday it did not have the hard evidence to support the intelligence collected.
Det Insp Robbie Paul said: "We believe we have an accurate intelligence picture of the group of people involved in carrying out the murder, but we can't go to court with intelligence alone. We need firm evidence.
"I'm fairly sure we know the group of people involved," he said, adding that the members of the gang could have carried out other attacks since.
"I have no doubt that they are committed members of a terrorist organisation and could be involved in other terrorist crimes. We believe David was not the specific target. This device was left for the first person who picked it up and it could have killed any of the mixed workforce," Det Insp Paul said.
"He was a decent hard-working man respected by his employers and a totally innocent victim of an organisation who have no role in a civilised society."
The DUP's Mr Gregory Campbell, the East Derry MP, said yesterday: "If the police are saying they know who is responsible but don't have the necessary forensic evidence to bring them to justice, then this is a serious indictment of our system of justice.
"Here we are a year later, and the people who carried out this atrocity are still walking about free." The murder of Mr Caldwell had a direct bearing on the political process at the time.
Mr Martin McGuinness, Sinn Féin's chief negotiator and a native of the city where the murder took place, was especially critical.
He insisted that at the time Sinn Féin's goals were to establish the primacy of politics and thus bring about the end of dissident republican violence.
The attack came at a time of concerted dissident attacks in Britain and against recruits to the PSNI which had been established only nine months before.
The investigation into David Caldwell's murder has symbolic status for all on the pro-agreement side.
Mr Caldwell was a soft target, and the Territorial Army base where he was murdered had no military significance and was used for the training of medical personnel.
Police officers set up road- blocks near the scene of the murder in Derry yesterday in an attempt to find new evidence.