Families of the victims and survivors of the 1972 Bloody Sunday, in which British soldiers opened fire and killed 13 unarmed civil rights marchers and injured 15 others in Northern Ireland, have fought for justice for five decades without a single person being held accountable in court. The ex-paratrooper, identified only as a “Soldier F” and concealed from view in court behind blue floor-to-ceiling curtain to protect him from vengeance, is the lone defendant in the deadliest shooting in the three decades of Northern Ireland violence known as “The Troubles.” The Jan. 30, 1972 massacre in Londonderry has come to symbolize the long-running conflict between mainly Catholic supporters of a united Ireland and predominantly Protestant forces that wanted to remain part of the United Kingdom.