One former British soldier will be prosecuted for two murders in the Bloody Sunday killings of 13 unarmed civil rights marchers in Derry.
The evidence was insufficient to charge 16 other former soldiers, Northern Ireland's Public Prosecution Service (PPS) said yesterday.
Soldiers from the Parachute Regiment opened fire on January 30, 1972, during an unauthorised march in the Bogside. They killed 13 people and wounded 14 others, one of whom died later.
A judicial inquiry said in 2010 the victims posed no threat to the military. It was the worst single shooting incident of the Troubles.
Stephen Herron, director of Public Prosecutions for Northern Ireland, announced that there was sufficient evidence to prosecute Soldier F for the murder of James Wray and William McKinney and for the attempted murders of Joseph Friel, Michael Quinn, Joe Mahon and Patrick O'Donnell.
However, "in respect of the other 18 suspects, including 16 former soldiers and two alleged Official IRA members, it has been concluded that the available evidence is insufficient to provide a reasonable prospect of conviction", he added.
Victims' families said they were disappointed, and their lawyers said they would challenge in the High Court any prosecutorial decision that did not withstand scrutiny.
"We would like to remind everyone that no prosecution, or if it comes to it, no conviction, does not mean not guilty, it does not mean that no crime was committed, it does not mean that those soldiers acted in a dignified and appropriate way," said Mickey McKinney, a brother of one of the victims.
Before a prosecution service briefing in the City Hotel, the families marched from the Bogside and sang civil rights anthem We Shall Overcome.
Mr Herron said he was conscious that relatives faced an "extremely difficult day".
"However, much of the material which was available for consideration by the inquiry is not admissible in criminal proceedings, due to strict rules of evidence that apply," he said.
The British government said it would provide full legal support to Soldier F.
"The welfare of our former service personnel is of the utmost importance," the UK's Defence Secretary Gavin Will- iamson said. "Our serving and former personnel cannot live in constant fear of prosecution."
Tanaiste Simon Coveney said it was important that no one said anything to prejudice the process following yesterday's decision, adding that his thoughts were with all of the families.
The Saville Report, which was published in 2010 after a 12-year inquiry, reversed the findings of a hastily-convened inquiry from 1972 by Lord Widgery, who concluded that the soldiers fired only after being fired on.
Supporters of the paratroopers say they were acting under extremely confused and stressful conditions, and it is unfair to pursue them so long after the event when many suspected IRA bombers and gunmen have been told they will no longer face arrest under the 1998 Good Friday Agreement.
Victims' families and other voices say they must nonetheless be held to account for their actions.
The decision to prosecute came a week after Northern Secretary Karen Bradley was forced to apologise for saying that killings by British soldiers and police were "not crimes".
Sinn Fein said it shared the families' disappointment and "sense of incredulity" at the PPS's decision.
"The decision to prosecute just one ex-soldier does not change the fact that Bloody Sunday was a massacre of innocents," said Sinn Fein's Northern Ireland leader, Michelle O'Neill.