text: Thirteen people were killed when British paratroopers opened fire on a civil rights march through the city in January 1972. A fourteenth died later.
  The 66-year-old former paratrooper was arrested in County Antrim on Tuesday.
  It is understood he is being questioned over the deaths of William Nash, Michael McDaid and John Young.
  He is soldier J, who was one of the soldiers who appeared before the Saville Inquiry.
  Leo Young, whose brother John was killed aged 17 on Bloody Sunday, told BBC Radio Foyle that he welcomed the news.
  "A flood of emotions came into my head when I heard the news about the arrest," said Mr Young.
  "A prosecution has to happen soon. We waited for over 40 years and this is a big step.
  "I think about my brother every day. His life was cut short and I keep thinking about him because he would probably be married today.
  "I was 24 at the time and going through those inquires was a real battle.
  "This is a giant step and I feel for all the families involved."
  John Kelly, whose brother Michael was among those killed on Bloody Sunday, said the arrest "gives fresh hope".
  "This is a massive moment for the families and the city," said Mr Kelly.
  "My brother's death is no different to any other death on that day. This is major development and I hope there is an arrest in relation to my brother soon.
  "Hopefully there will be prosecutions soon."
  Sir Gerald Howarth, a Conservative MP and former defence minister who represents former soldiers on duty at the time of Bloody Sunday, said there are hundreds of families dealing with murder across Northern Ireland.
  "We cannot forget that a lot of families haven't had justice yet," said Sir Howarth.
  "It would be good if we could just close this chapter.
  "I'm not excusing what happened but I do not think it is in the public interest for former soldiers to be prosecuted.
  "This is now a matter for the prosecuting authorities though."
target: Detectives are continuing to question a former soldier over the deaths of three people on Bloody Sunday in Londonderry.