Six men were shot dead in the bar
A PSNI officer has been arrested and questioned over allegations of misconduct around the investigation of the Loughinisland atrocity.
The arrest was made by detectives from the police ombudsman's office.
Six men were shot dead in the UVF gun attack on the Heights Bar in 1994.
The reserve constable is understood to have been detained earlier this week and has since been released pending further enquiries.
Families of the victims pressed the ombudsman to take action amid claims of serious flaws in the original RUC investigation into the killings.
One of the victims, Barney Green, 87, was one of the oldest people to be murdered during the Troubles.
The others who died were Adrian Rogan, 34; Daniel McCreanor, 59; Eamon Byrne, 39; his brother-in-law Patrick O'Hare, 35, and 53-year-old Malcolm Jenkinson.
Five people were also injured in the attack by gunmen armed with an AK47 and a Czech-made rifle.
No one has been convicted over the killings.