Bloody Sunday: What caused landmark legacy prosecutions to collapse?

A plaque on the spot where Joe McCann was shot dead in April 1972 (PA)

An admissibility ruling by a judge in the trial of two former soldiers accused of a Troubles murder has triggered a chain of events that has led to the halting of two further legacy cases in Northern Ireland, including the only prosecution ever mounted over the notorious Bloody Sunday killings of 1972.

Here is an explanation of why the controversial prosecutions have unravelled.