Police in Northern Ireland questioning three men over the murder of constable Ronan Kerr fear further attacks on their officers are being planned.
A 33-year-old man was detained in the Omagh area on Friday over the booby trap bomb attack that killed the 25-year-old Catholic officer outside his home in the Co Tyrone town on Saturday.
Police were on Friday also given five more days to question a 26-year-old man arrested in Scotland on Wednesday and re-arrested on Thursday, plus a 40-year-old man arrested near Omagh on Thursday.
The under-car bomb was blamed on dissident republicans who remain violently opposed to the peace process.
It has also emerged that the groups are continuing to target policemen in the wake of Pc Kerr's murder.
Senior police sources have said the public outcry following the young officer's death has had no influence on the mindset of extremists, who remain focused on killing members of the security forces.
Detectives have evidence the dissidents have been actively targeting Police Service of Northern Ireland (PSNI) personnel since the weekend murder.
Officers do not want the nature of the intelligence to be made public for investigative reasons, but they say murder plots are being uncovered at a rate of one a fortnight. One PSNI source added: "There is absolutely no indication the community outrage has had any impact on the mindset of the dissidents."
In a further development, it has emerged that just 24 hours before the fatal car bomb blast in Omagh, police had ordered a specialist team of detectives to begin sifting through evidence from historic dissident attacks in a bid to ramp-up the pressure on the terrorists. The cold case review will see exhibits analysed using the latest fingerprint recognition technology and Low Copy Number (LCN) DNA forensic techniques.
The review will examine specific crimes detectives believe may have involved present-day dissidents. However, the team will not confine its work to terror acts and every facet of suspected dissidents' affairs will be examined, from past financial dealings to potential involvement in other crimes.