A Belfast man shot and injured in the Sean Graham’s massacre has described the moment when families were told the murder weapon was on display in a British museum.

Mark Sykes, who was shot in the attack that killed his teenage brother-in-law Peter Magee, was speaking after last week’s BBC Panorama programme on security force collusion revealed the rifle used in the atrocity had not been destroyed, as claimed, but was on display in the Imperial War Museum in London.

Five people – Jack Duffin (66); Willie McManus (54); Christy Doherty (52); Peter Magee (18); and James Kennedy (15) – were gunned down by a loyalist murder gang in broad daylight in February 1992.

Families had long believed the V758 rifle used in the killings had been destroyed.

It was only when they attending a seemingly routine meeting with the Police Ombudsman’s office that they discovered that not only was the weapon still intact but it was on open display in London.

“As a group of families we each have a representative who meet with the people we need to meet with on a regular basis,” Mark said.

“This has ben going on for so long you almost become desensitised to what you keep hearing. We were at that meeting expecting an update but then we were told that not only had they found it but also that it was in the Imperial War Museum – there was just total silence. “We all just looked at each other. We had long thought it was destroyed. Imagine going back and telling the rest of the families this. Some of the wives and mothers of those killed are in their 80s. Imagine how that made them feel.”

The families and victims’ group Relatives for Justice have long exposed the extent of collusion in the killings.

In September 2010 an investigation by the Historical Enquiries Team (HET) revealed UDA informer William Stobie had handed the Browning pistol used in the attack over to RUC officers, only for them to return it to the loyalist group.

The Browning pistol and the rifle used in the Sean Graham’s attack were both part of a consignment imported from South Africa in 1987 by UDA double agent Brian Nelson that was not stopped by his British army handlers.

On December 22, 1991, the same pistol was used to murder 22-year-old Aidan Wallace in an attack at the Devenish Arms as he played snooker with his brother. Three other people were injured during that attack, including an eight-year-old boy who lost an eye. The pistol was then handed back to loyalists for use in the bookies massacre.

Mark Sykes said every new piece of evidence uncovered in the families’ search for truth indicates systematic evidence of collusion and that the killings could have easily been prevented.

“It’s galling to think that these men who ordered the handlers and the agents to do this are now sitting with big pensions and pay-outs.

‘They might be telling their children and grandchildren about their role fighting republicans here. Are they telling them they helped kill two young boys in a shop? That they helped what are essentially psychopathic killers?

“The murders could have been prevented at a number of turns but nothing was done. We want those who allowed this to happen to be held to account.”