A retired British soldier has been arrested by detectives investigating the shooting of a man with learning difficulties in the North in 1974.
John Pat Cunningham, 27, was shot by the Army in a field in Benburb, Co Armagh.
The 73-year-old suspect was detained in England. He is being taken to Northern Ireland for questioning at the police's Serious Crime Suite in Antrim.
The case was re-opened by the Police Service of Northern Ireland and a murder investigation started following a re-examination of the available evidence.
Mr Cunningham had a fear of men in uniform and was running away from an Army patrol when he was shot.
The British government apologised for his death in 2013.
The inquiry is being carried out by the PSNI's Legacy Investigations Branch - a unit which examines historic cases from the Troubles.
Relatives of Mr Cunningham, who had a mental age of between six and 10, said the investigation did not have their support.
Victims campaign organisation the Pat Finucane Centre (PFC) issued a statement on the family's behalf.
"Whilst family members have cautiously welcomed the arrest, they have asked the PFC to state categorically that they will only have confidence in an investigative process that is completely independent of the PSNI," said a PFC spokesman.
"Cunningham family members said in October 2013 that they wish to see all investigations into British Army killings, including that of John Pat, being investigated by an independent body."