The murderers of PSNI officer Ronan Kerr are waging "a useless war against peace", the NI Deputy First Minister Martin McGuinness has said.
He was speaking after meeting PSNI chief Matt Baggott with First Minister Peter Robinson and Justice Minister David Ford on Monday.
Constable Kerr, 25, was killed by a bomb which exploded under his car outside his Omagh home on Saturday.
Police believe dissident republicans were responsible for the attack.
No arrests have been made.
Mr Robinson told the press conference that the County Tyrone attack had "strengthened institutions, united our community and brought politicians closer together".
Chief Constable Baggott said he would not provide details of the police investigation but that the senior investigating officer may speak later on Monday.
Dissident republicans oppose the police service and have targeted officers in both gun and bomb attacks.
Mr Kerr is the second police officer to have been murdered since the Royal Ulster Constabulary became the PSNI in 2001.
He joined the police in May 2010 and had been working in the community since December.
He played Gaelic football for his local club and his murder has been condemned by the Gaelic Athletic Association.