Most of the suspects in the murder of Paul Quinn live in Northern Ireland, the Policing Board has been told.
Mr Quinn was found at farm buildings near the village of Oram
The 21-year-old Cullyhanna man died after being severely beaten in County Monaghan almost two weeks ago.
The board was told as Mr Quinn was attacked and found in the Republic it was a Garda investigation.
However, Deputy Chief Constable Paul Leighton said there was day-to-day co-operation between the PSNI and Garda on it.
The DUP's Jeffrey Donaldson said he was concerned there were no reports of arrests on either side of the border.
DCC Leighton said he did not want to give many more details because he did not want to prejudice what was essentially a Garda investigation.
However, Mr Donaldson continued to press, saying the case had political implications.
Assistant Chief Constable Peter Sheridan did then give some more information about the investigation.
"For the most part, most of the witnesses, the suspects and so on will be on this side of the border, when in actual fact to a large extent it was on the southern side of the border where there is a crime scene," he said.
A gang of up to nine men was involved in Mr Quinn's killing.
His family have blamed it on the IRA. They said he had defied an order to leave the country.
Sinn Fein has denied republican involvement.