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 yesterday 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 yesterday 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.
"We hope to engender a state of paranoia among the dissidents," said another police source. "Make their lives as uncomfortable as possible."
None of the renegade groups has yet claimed responsibility for the murder of Pc Kerr.
But officers have indicated that increasing links and co-operation between disparate organisations means a specific claim is not as relevant to their investigation as it might once have been.
They believe there are nearly as many as 30 distinct groupings operating across Northern Ireland, some claiming to be the Real IRA, some Continuity IRA, some from Oglaigh na hEireann, with other groups claiming no affiliation at all.
The fluid nature of the dissidents has seen a new grouping emerge in the Co Tyrone area in recent months.
The first two men arrested in connection with Pc Kerr's murder are being questioned at Antrim police station.
The 40-year-old and 26-year-old are also being quizzed about a substantial arms and explosives cache uncovered by the murder investigation team near Coalisland, Co Tyrone, on Tuesday night.