Twenty-five years ago, Sunday World journalist Martin O’Hagan was shot dead as he walked home with his wife in Lurgan, Co Armagh.A fearless investigative reporter who exposed the criminal underworld behind Northern Ireland’s paramilitaries, O’Hagan had made dangerous enemies on both sides, but no one has ever been convicted of his murder.Joining Fionnán Sheehan on the Indo Daily is Sunday World Northern editor Richard Sullivan and Irish Independ…