Gavin McShane and his friend Shane McArdle were murdered by the UVF in a sectarian gun attack in Armagh in 1994.Seventeen-year-old Gavin was playing a video game in a taxi depot in Armagh when he was gunned down.No one has ever been brought to justice for killing the two schoolboys.The family, ahead of the anniversary of the killing on Sunday, have told UTV they are taking a civil action against PSNI Chief Constable Matt Baggott over the destruction of the evidence.Items including clothing that Gavin was wearing at the time of his death were incinerated.Gavin's mother Maria told UTV: "Evidence was destroyed, but ballistics have moved on."Recently a case was won on the evidence from a butt of a cigarette that was held and that put someone behind bars."Simple things like that, forensics have moved on so much, there could have been something on Gavin's clothes."She added: "The police promised me that they would leave no stone unturned, that they would get who murdered my Gavin and I believed them."A man, with no mask on, walked across the street, put a gun to my child's head and away he went."The police know who it was."Maria says she is determined to get those responsible to pay for the crimes they committed.She added: "I'll keep trying, I am not going to stop, I will be a thorn in their side and I am coming to get you."I will put that boy behind bars."The family are also asking the Police Ombudsman to investigate the RUC's handling of the investigation.The PSNI has not commented on the case.