Nine undercover soldiers were at the scene of a killing claimed by the UVF in Lurgan, a new report has revealed.
The Historical Enquiries Team (HET) report centres on an incident where three republicans were ambushed minutes after they left a police station on 7 March 1990.
Former republican prisoner Sam Marshall was killed in the incident.
The HET praised much of the original RUC investigation and found no new lines of inquiry on the gun attack.
The presence near the scene of a red Maestro car, later found to be a military intelligence vehicle, led to claims of a security force role in the killing.
It has emerged the car was one of six vehicles in a major surveillance operation involving eight armed undercover soldiers.
Although the loyalist killers launched the attack within yards of armed troops and escaped, investigators said there was no evidence of state collusion with the gunmen, and no evidence that any police officer or soldier had prior knowledge of the attack.
A review of the case by the HET has now found:
- At least eight undercover soldiers were deployed near the killing, with their commander monitoring from a remote location.
- The armed military personnel at the scene were in six cars, including the red Maestro.
- Two plainclothed soldiers with camera equipment were in an observation post at the entrance to the police station as the three republicans arrived and left.
- The killers' two guns were never recovered, but were linked through ballistic tests to three other murders and an attempted murder.
- Intelligence also linked a further murder to Mr Marshall's murder.
- Two soldiers followed the three men on foot when they left the police station, and "partially witnessed" the shooting.
The Marshall family has said the review of the case - which did not reinterview the soldiers but relied on RUC statements from the time - has only served to raise further questions.
Sam Marshall, his brother-in-law Tony McCaughey, and Colin Duffy, were known to the security forces and were high-profile republicans.
John Marshall, a brother of the 31-year-old murder victim, said: "The gunmen meant to kill the three men that night, and it went wrong.
"The other two guys lived to tell the tale."
Sam Marshall, who was a Sinn Fein member, was sentenced to seven years for arson as a teenager and took part in IRA protests for political status while he was held in the Maze prison.
A police investigation into a robbery in Belfast led to the arrest of two loyalists later convicted for supplying the killers' car.
The gunmen have never been identified.