There were "significant failures" in the police investigation into the murder of a Catholic teenager by loyalist paramilitaries, a Police Ombudsman's report has concluded.
Damien Walsh was shot in 1993.
There was no evidence police had advance knowledge of the attack or could have stopped it, the report said.
But there were "collusive police behaviours" in the investigation and decision to suspend surveillance of the gang responsible.
The teenager was fatally wounded after being shot by the UDA (Ulster Defence Association) in Belfast.
He was at work at a coal supply business within the Dairy Farm shopping complex close to Twinbrook in the west of the city.
At the time, the complex was under security force surveillance - fertiliser for Provisional IRA bombs was being stored in a premises two doors away from the coal business.
Ombudsman Marie Anderson said the teenager was "the innocent victim of a terror campaign mounted by loyalist paramilitaries against the nationalist community".
"The UDA alone were responsible for Damien's murder," she added.
"However, I have identified investigative failings and gaps as well as collusive behaviours by police, which I believe failed both Damien and his family."
Ms Anderson noted that in the days before the shooting, the Royal Ulster Constabulary (RUC) suspended a surveillance operation against the UDA's 'C company'.
She said the decision "cannot be directly linked to Damien's murder", but it "indirectly contributed" to them being able to operate without constraint.
"In my view this amounted to a deliberate decision that constituted collusive behaviour on the part of police."
During the period when the gang was not under watch, it also murdered Peter Gallagher at the Westlink Enterprise Centre in west Belfast.
Ms Anderson's report said police had suspended their surveillance in order to focus resources on the operation against the IRA at the Dairy Farm.
Her report also found major failures in the murder investigation.
The senior investigating officer was not told of the surveillance operation of the Dairy Farm complex, nor was he made aware of Army witnesses to the attack.
Ms Anderson found this was a deliberate decision to impede the investigation.
"Intelligence indicating the UDA had received information from a police officer which informed their attack on the Dairy Farm was also withheld from the senior investigating officer, as was intelligence suggesting that the group had received information from 'British intelligence'."
The report stated the targeted nature of the attack, near a business unit being used by the IRA, "suggested that gunmen had prior knowledge of the PIRA activities at the Dairy Farm".
The ombudsman further found that of seven suspects, just three were arrested and only one questioned in relation to the murder.
None of the three suspects' homes was searched for evidence and no one has ever been charged in relation to the murder.
Police also failed to pursue evidence relating to the murder weapon.
The Browning pistol was found a year later but the person caught with it was not subjected to forensic tests to determine whether he could be linked to the teenager's killing.
Neither was the man he claimed had given him the weapon.
The gun was subsequently destroyed - something which Ms Anderson said ought not to have occurred in an unsolved murder case - although its disposal was in line with police policy at the time.
All police officers connected to the case are now retired.
'Totally wrong and totally immoral'
The Walsh family welcomed the ombudsman's findings and said they are determined to continue to fight for those involved to face justice.
"His life was stolen from him," said Damien's mother Marian.
"I am glad that all the suspicions I had around collusion have been verified at an official level.
"I really want to go on with this and I want to see the people who did this brought to court."
Speaking to the BBC's Good Morning Ulster programme, Ms Walsh said she was "really exhausted, physically and mentally".
Ms Walsh described government plans announced last week, which would see an end to Troubles-related prosecutions, as "totally wrong and totally immoral".
"This should just be the beginning of the process and I'm hoping it will be, but given Boris Johnson's trying to bring in legislation to stop any further investigations or prosecutions, inquests and so on, it looks like it might be the end of the process.
"It's denying us our basic human rights, we have the right to justice, we have the right to truth and that is taking all of that away."
Police Service of Northern Ireland (PSNI) Assistant Chief Constable Jonathan Roberts said the service would carefully consider the Police Ombudsman's report with a view to identifying appropriate next steps.
"Damien Walsh was an innocent young man killed by a despicable act of terrorism," he said.
"The pain of such a grievous loss does not fade and I am acutely aware that today will be very upsetting for the family. My thoughts are with them."