He presided over an external police inquiry into allegations in Northern Ireland of collusion between the British Army, the Royal Ulster Constabulary and loyalist terrorists to help in the murder of Northern Ireland nationalists. Stevens' third report, published on 17 April 2003 upheld the claim and explicitly said that collusion leading to the murder of Northern nationalists (and some unionists wrongly throught to be catholic or nationalist) had taken place. In the aftermath of his shock report, David Trimble, the leader of Ulster Unionist Party called for a parliamentary inquiry into the collusion, while the leaders of the Social Democratic and Labour Party and Sinn Féin called for a full public inquiry.