The 2005 murder of Robert McCartney put the entire peace process in jeopardy.
The 32-year-old was beaten and stabbed after attempting to stop a row in Magennis's Bar in Belfast.
The full truth of what happened is unlikely to ever be known despite a campaign for justice by his sisters and fiancée - but Gerard 'Jock' Davison is believed to have run a finger across his throat to order an attack on McCartney.
His family turned international opinion against Sinn Féin and the White House withdrew its invitation to Gerry Adams to attend on St Patrick's Day in 2005.
After initially denying that any of their supporters had been involved, Sinn Féin and the IRA later admitted to suspending 12 party members and the expulsion of three IRA members, including Davison.
In her book, 'Walls of Silence', the murdered man's sister, Catherine, accused the Provo boss of ordering an attack on her brother.
After being attacked in the pub, Robert had fled with two friends.
Davison was alleged to have ordered a number of Republicans to follow them.
McCartney and another man had their throats cut and were left lying on the street. When police arrived to investigate, Davison and other leading Republicans were suspected of organising an impromptu riot that forced the police to retreat.
Magennis's Bar was described as having been forensically cleaned and all CCTV tapes had been removed by the time police finally moved in to investigate.