Ronan Kerr murder 'brutal and grotesque'
The police officer killed by a bomb in Omagh on Saturday was "brutally and grotesquely murdered" a detective leading the investigation has said.
Detective Superintendent Raymond Murray said the bomb which killed Constable Ronan Kerr was probably up to a pound in weight.
It was inside a plastic box which had been attached under his car.
Chief Superintendent Murray said it had been probably detonated by a tilt switch, which is set off by movement.
He said police believed it was planted some time between Thursday evening and when it exploded on Saturday afternoon.
Constable Kerr, 25, was killed outside his home in the Highfield estate.
Chief Supt Murray said components of the bomb had been recovered.
It also contained a timing mechanism which may have been for the safety of the bombers while they moved the device.
He would not be drawn on which group he thought was responsible, however he said there had been a number of dissident republican threats in the Omagh area recently.
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.
Earlier, NI Deputy First Minister Martin McGuinness said Constable Kerr's killers were waging "a useless war against peace".
He was speaking after meeting PSNI chief Matt Baggott with First Minister Peter Robinson and Justice Minister David Ford on Monday.
Mr Robinson told the press conference that the County Tyrone attack had "strengthened institutions, united our community and brought politicians closer together".
Dissident republicans oppose the police service and have targeted officers in both gun and bomb attacks.
Constable Kerr played Gaelic football for his local club and his murder has been condemned by the Gaelic Athletic Association.
Tyrone Gaelic footballers held a minute's silence before a match against Kildare at the weekend.
His mother, Nuala, has since urged Catholics not to be deterred from joining the PSNI.
Mr McGuinness said dissident republicans engaged in violence were "enemies of the peace, enemies of the people of Ireland".
He added that many young nationalists and republicans had joined the police and said he was "as proud of them as Nuala Kerr was of Ronan".
He said he was completely united with Mr Robinson in his support for the police.
"We are not going away. We represent the people. I represent the people of County Tyrone. I represent the people of Ireland," Mr McGuinness said.
"We are the people who will prevail."
Police have set up a dedicated phone line for anyone with information on the murder to contact them.
The number is 028 82 256659.