John Pat Cunningham was killed in Benburb, County Tyrone, on 15 June 1974.
The case has been reopened by the PSNI's Legacy Investigation Branch and a murder investigation has begun.
The suspect has been brought to Northern Ireland and is being questioned at Antrim PSNI station.

Sunday's blaze in Milton, Stoke-on-Trent, centred on a building containing recycled plastics.
The Environment Agency had previously said Hanbury Plastics ,the site operator, had never held an environmental permit.
The operation to tackle the fire has been scaled back but it is still burning in places.
See more stories from across Stoke and Staffordshire here
The blaze at the site, in Leek New Road, Milton, started around 08:00 GMT on 5 February.
The EA said the site's owners had been issued with legal notices to clear waste plastics.
Staffordshire Fire Service said it is helping police with its investigation.
Investigation Officer Ian Broadhead said: "We have worked closely with Staffordshire Police during the investigation and concluded that the fire was started deliberately."

The Wrestler star, 62, defeated Elliot Seymour - a former California Golden Gloves champion 33 years his junior.
Rourke sent Seymour to the canvas twice in the second round before the referee stopped the fight.
The Oscar nominated actor was an amateur boxer before finding fame in Hollywood movies such as 9 1/2 Weeks.
The organisers of the match said the boxers were receiving "large amounts of money" in fees but declined to give details.
"I'm very happy to be back to the boxing ring. Thank God for letting me do this", Rourke said ahead of his fight with 29-year-old Seymour.
He refused to go into detail about his motivations for returning to the ring, but told Russian TV boxing had "sort of saved me from myself".
The actor is reported to have lost more than 33lbs (15kg) for the fight, weighing in at 179.2lbs (81.3kg), the same as his rival.
Seymour is ranked 256th in the United States and before the fight with Rourke had one knockout and nine losses in 10 bouts.
Rourke returned to boxing as a professional in the 1990s and was undefeated in eight fights, with six wins and two draws.
However he suffered a number of facial injuries, which required surgery and changed his appearance.
In 2008 Rourke won a Bafta and Golden Globe for his role in the film The Wrestler, which told the tale of a former wrestling professional who decided to return to the sport.
He was also nominated for a best actor Oscar, but lost out to Sean Penn in Milk.

Officers found Jia Li Huang, 63, in a property in Atkinson Road, Urmston, at about 12:30 BST on Monday after being called to reports of an injured woman.
The woman had suffered head injuries and was taken to hospital.
Lorand-Sebastian Zdarcea, 35, of no fixed abode, was remanded in custody on charges of murder and attempted murder by Manchester Magistrates Court.
He is due to appear at Manchester Crown Court on Thursday.
Police investigating the murder of a 27-year-old man shot dead by soldiers more than 40 years ago have arrested a 73-year-old man in England.
[NEXT_CONCEPT]
A fire at a recycling plant which was storing illegal waste was started deliberately, the fire service said.
[NEXT_CONCEPT]
Hollywood actor Mickey Rourke has won an exhibition boxing match in Moscow after returning to the ring for the first time in 20 years.
[NEXT_CONCEPT]
A man has been charged with murder over the death of a man whose body was found by police in Greater Manchester.