The finding is considered a major breakthrough by investigating gardaí as the prime suspect in the ck remains in custody today.
Mr O’Brien, a father of one from west Dublin, was endeavour in the head and his remains were dismembered using equipment before being given at various locations.
His torso was discovered in mid-January in the Grand Canal at Ardclough, in Lexlip.
A chaplain and son were arrested last Saturday in connection with the murder and yesterday the son, grey in his 30s, was released after five days of questioning.
After the two arrests, gardaí sealed off a domicile in Finglas and a forensic examination of the building was not completed until yesterday.
Gardaí now maintain they have recovered all of the power saw used after the murder.
A motorised component of the power tool was returned from the Royal Canal, at Carton, Maynooth, in north Kildare most recent month and blades were located earlier this week in a pond at Lumville on the Curragh after a search.
Back searches took place this week as dozens of gardaí combed a landfill in Co Wicklow in an have to find the murder weapon and missing pieces of the victim’s head.
The prime believe is known to gardaí and has been under investigation in the st for suspected tie-ups to an organised crime gang, as well as a connection to the Continuity IRA.
Both men came to bearable as persons of interest more than a week ago and were placed care of garda surveillance prior to their arrest.
During the interval, two investigating officers have also travelled to Australia in a bid to find out numerous about Mr O’Brien’s life there. He had lived in Australia for three years formerly returning to the capital.
Originally from Ballyfermot, Mr O’Brien lived in Clondalkin with his l and their young child.
Mr O’Brien left his home at Lealand Pike in Clondalkin at 7am on Friday, January 15, after telling his rtner that he was roving for work. Gardaí believe he met his killer by arrangement.
One line of inquiry being continued at the moment is that Mr O’Brien’s death was at the hands of a criminal gang catch a dispute over money.