The 66-year-old ex-paratrooper, detained in Co Antrim yesterday, was the first person arrested by detectives probing the deaths of the 14 people killed after the Parachute Regiment opened fire on crowds of protesters in the Bogside in January 1972.
It is understood the pensioner is being questioned about the deaths of William Nash, 19, John Young, 17, and Michael McDaid, 20, all of whom were shot dead in close proximity to one another at a rubble barricade on Rossville Street.
It is believed the former soldier is also being questioned about the shooting of William Nash’s father, Alexander. Mr Nash came to the barrier to save his son and was wounded in the arm and body, but survived.
It is understood the soldier gave evidence to the British government-commissioned inquiry into Bloody Sunday, undertaken by Lord Saville, under the cipher ‘Lance Corporal J’.
Kate Nash, William’s sister, welcomed the development.
“We have always fought very hard to be treated equally within the justice system,” she said. “I see this as a positive step.”
Thirteen people were killed on the day of the incident. Another victim of the shootings died in hospital four months later.
The Police Service of Northern Ireland’s murder investigation into the events of Bloody Sunday was launched in 2012.
The probe was initiated after the Saville Inquiry found none of the victims had posed a threat to soldiers when they were shot.
Following the publication of the Saville report in 2010, British prime minister David Cameron apologised for the British Army’s actions, branding them “unjustified and unjustifiable”.
In September, the PSNI announced their intention to interview seven former soldiers about their involvement. The suspect detained by the PSNI’s Legacy Investigations Branch was taken to a police station in Belfast for questioning.