An inquiry into alleged Garda collusion in the IRA murders of two senior Northern Ireland police officers could be thwarted over a lack of witnesses, it has been warned.
A lawyer for the family of the late RUC Supt Bob Buchanan said a number of former and serving RUC and PSNI officers with valuable information have yet to testify before the Smithwick Tribunal.
The inquiry is expected to finish hearing evidence next month.
Solicitor Ernie Waterworth said without their attendance the investigation may find it impossible to make firm conclusions.
Inquiry chairman Judge Peter Smithwick is investigating the ambush of Supt Buchanan and RUC Chief Superintendent Harry Breen after leaving a meeting in Dundalk Garda station on March 20, 1989.
"The Buchanan family greatly appreciate the considerable assistance which has been provided by both retired and serving members of the RUC/PSNI," said Mr Waterworth.
"However, a number of former police RUC/PSNI officers and serving PSNI officers hold valuable information that would be of assistance to this tribunal.
"Some have been unable to attend for different reasons. There are also others who may not realise the importance of the information they possess," he said.