The Police Service of Northern Ireland has confirmed it is to launch a murder inquiry into Bloody Sunday, where 13 people were shot dead by British soldiers in 1972.
The investigation, which may involve up 30 police staff and could last up to four years, follows the Saville Inquiry's report into the deaths.
That report said civil rights demonstrators killed by troops in Londonderry at the height of the Troubles were innocent.
Soldiers opened fire on marchers during a civil rights march on January 30, 1972.
Lord Saville's report blamed the Army for one of the most controversial days in Northern Ireland's history.
Key findings included: No warning had been given to any civilians before the soldiers opened fire, and none of the soldiers fired in response to attacks by petrol bombers or stone throwers.
The report also found some of those killed or injured were clearly fleeing or going to help those injured or dying.
It said none of the casualties was posing a threat or doing anything that would justify their shooting and many of the soldiers lied about their actions.
It added Northern Ireland's Deputy First Minister Martin McGuinness of Sinn Fein was present at the time of the violence and "probably armed with a sub-machine gun" but did not engage in "any activity that provided any of the soldiers with any justification for opening fire".
Chief Constable Matt Baggott said matters contained in the report should be investigated but asked what the consequences were for keeping people safe now if detectives were diverted from today's crimes.