Concern is growing in Northern Ireland that a new dissident Republican group may have carried out the murder of police constable Ronan Kerr.
Both the Continuity IRA and the Real IRA have bomb making experience of the kind used in the attack, but neither group has claimed responsibility for the murder of the 25 year old constable.
Now, according to a report in the Herald, fears are growing that a group of disaffected republicans that have recently left the mainstream IRA in Tyrone may be responsible for the attack.
"We have real concerns about that area. There are serious concerns about leakage," a source with knowledge of intelligence assessments told the Herald.
The source could not confirm if those who have left the IRA have joined with one of the dissident groups.
A senior republican quoted in the Herald suggested that the dissidents may have been taken aback by the storm of condemnation that followed the weekend killing.
"It's interesting thus far that nobody has popped their head up to defend what happened or explain what happened," the source was quoted as saying. "I don't think they anticipated the backlash. They probably hadn't thought about it. It may give them cause to think," he said.