Three people remain in custody in connection with the murder of Kenneth Fetherston (26) whose body was found in Dublin mountains last month.
The father-of-one had been missing for four months before his remains were discovered in a boggy ditch off Military Road in Rathfarnham in January.
Gardaí believe Mr Fetherston may have been killed when he sought the return of money he had given to somebody known to him.
A man and a woman, both in their 40s, were arrested yesterday morning in Dublin and Wexford.
A further two men were arrested at unspecified locations this morning. The four were being questioned by detectives at Tallaght and Rathfarnham Garda stations. One man was released from custody earlier this evening.
Gardaí do not believe Mr Fetherston was involved in any criminal activity
He was last seen on September 22nd, 2009 at Landy's Industrial Estate on the Knocklyon Road in Dublin.
He had been driving a red Honda Civic, registration number 93 D 44862, which was found in a layby on the N11 near Gorey, Co Wexford four days later.
He left his apartment at the Tallaght Cross Hotel shortly before 9am that morning.