Irish police have apologised to the PSNI for questioning journalists in NI about the murder of a former Sinn Fein official without informing them.
Gardai said people interviewed had not been connected with the crime, but were spoken to in case they had information which could help detectives.
They said the failure to inform the PSNI in advance was an oversight.
A PSNI spokesman, accepting the apology, said co-operation between the two police forces remained high.
Mr Donaldson, 56, was found shot dead in a remote cottage in County Donegal earlier this month.
He had been expelled from the party in 2005 after admitting he was a paid British agent.
Mr Donaldson had been Sinn Fein's head of administration at Stormont before his 2002 arrest over alleged spying led to its collapse.
He and two others were acquitted of charges last December "in the public interest".
One week later he admitted being recruited in the 1980s as a paid British agent.
He said there had not been a republican spy ring at Stormont.