The family of an innocent Donegal teenager murdered by the loyalist paramilitary UVF 35 years ago have said detectives have found evidence of British security force collusion in the case.

Henry Cunningham, 16, from Carndonagh, died in August 1973 when loyalist gunmen ambushed the van he was in.

The details emerged after a fresh investigation by the Historical Enquiries Team.

The report said detectives uncovered evidence of collusion in the theft of a murder weapon from a British Army UDR base.

Henry Cunningham was travelling home on the M2 when UVF gunmen opened fire on the van from a motorway bridge.

His older brother Herbert, who was driving, was injured, but a third brother, Robert, was unhurt.

No one has been prosecuted for the murder, and the family believe the case was never fully investigated.

The brothers said the investigation had been a "long and painful process". "Many questions remain unanswered.

"The Historical Enquiries Team (HET) review has however provided us with some answers and with shocking new information about the circumstances of Henry's death," they said.

According to the report, one of the weapons used in the attack had been stolen from a UDR base in Lurgan in 1972.

The HET found evidence of collusion between loyalists and the security forces in the raid on the base.

Both murder weapons were recovered by the RUC in separate incidents in 1974, but despite being linked to a number of unsolved serious crimes, they were later destroyed by the RUC.

The HET also said that declassified documents noted that "there were high level concerns regarding RUC elements 'too close to the UVF' and 'too ready to hand over information', and worries that loyalist extremists had heavily infiltrated the UDR.

The report concluded that Henry Cunningham, other members of his family and work colleagues, were "specifically targeted as a group by the UVF in a pre-planned attack on 9 August 1973".

It said that it was likely they had been observed following a regular pattern, travelling on the M2 in a van with Republic of Ireland registration plates.

It also said they were all incorrectly identified as Catholics working in the construction industry.

Those in the van were both Catholic and Presbyterian.

"The ballistic linkage of one of the murder weapons to the double murder of Catholic workmen gives credence to this scenario," it said.