Kieran Greene has been found guilty of murdering grandmother-of-seven Patricia O'Connor, who he battered to death with a hurley and cut up with a hacksaw before scattering her remains in the Wicklow Mountains.
A jury delivered the unanimous verdict at the Central Criminal Court, after four hours and 24 minutes of deliberations, following a seven-week trial.
The jury is due to continue considering verdicts today in the cases of three other people accused of impeding Greene's prosecution for murder.
Greene (35), wearing a red anorak over a light grey tracksuit, sat with his hands clasped in front of him as the verdict was read out. He blinked rapidly and looked around, but otherwise showed no reaction.
Greene killed Patricia (61), mother of his then-partner Louise O'Connor, in a row in the bathroom at the family home they shared at Mountain View Park, Rathfarnham, on May 29, 2017.
He buried her body in a shallow grave in Co Wexford before digging it up 10 days later and dismembering it, dumping the pieces along a mountain road.
Greene was one of four people on trial over the retired hospital cleaner's death.
Patricia's daughter Louise (41), granddaughter Stephanie O'Connor (22) and Keith Johnston (43) are charged with impeding Greene's prosecution.
Greene was Louise's partner at the time, while Mr Johnston, Stephanie's father, was Louise's ex-boyfriend.
Stephanie O'Connor is accused of disguising herself as her grandmother after her murder to pretend that she was still alive, while her mother Louise is alleged to have agreed to this.
Mr Johnston is alleged to have assisted Greene in buying implements to use in the concealment of Patricia's remains. They all pleaded not guilty.
Before the trial started, Patricia's husband Gus O'Connor admitted falsely reporting she was missing on June 1, 2017, when he knew she was dead.
Yesterday afternoon, when the jury returned, Mr Justice Paul McDermott initially told the jurors to suspend deliberations for the day, but it then became apparent a verdict had been reached.
The jurors, who had got up to leave, were asked to take their seats again. The court registrar asked the forewoman if they had reached a verdict in any of the cases in which they were all agreed. "Yes," she replied.
The registrar said the verdict recorded on the issue paper on the one count against Greene was that he was guilty of murder. She asked if this was the verdict of all the jury.
"Yes," the forewoman replied.
The verdict was greeted by silence in the courtroom.
Judge McDermott then sent the jurors home for the night, to resume deliberations in the other cases today.
Patricia's dismembered remains were found strewn in 15 parts at nine locations over a 30km-wide area in the Wicklow Mountains between June 10 and 14, 2017. A post-mortem found she died of blunt-force trauma to the head caused by at least three blows from a solid implement. There were no defensive injuries.
Over the course of the trial, the jury heard that, while the body parts were still being recovered, Greene handed himself in to gardai and claimed he had killed Patricia in self-defence after a row at their home.
He told them it happened after she attacked him with a hurley in the bathroom; he disarmed her, hit her with it and they both fell, he said.
He blacked out and did not know what happened, but thought she probably banged her head on the tiles.
When he came to, there was "blood everywhere" and he dragged her upstairs to her room. He did not know if she was dead but she was not moving. He told gardai he brought the body to his car and drove it to a cornfield in Co Wexford, where he buried it in a shallow grave. Mr Greene said he panicked and returned on June 9 to move the body but he could not, so he cut it up with a hacksaw, brought the parts to Co Wicklow and scattered them.
Greene told gardai Patricia had been verbally abusive to the family "on a constant basis, always threatening to have us killed". He graphically described chopping the body up "a bit smaller to make her lighter", and how he "spewed into a bag".
When he had thrown the body parts away, he said: "I got back in the car and sobbed and sobbed. I just thought, 'My kids don't have to worry any more, I'm finally free'."
He said he acted alone at all times. However, six months later, he retracted this and told gardai it was Patricia's husband who killed her. He alleged Mr O'Connor intervened during the bathroom struggle and hit Patricia with a metal bar, then told him: "I'm defending you so you can take the rap for this."
Roisin Lacey SC, prosecuting, told the jury Greene inflicted "catastrophic injuries" on Patricia when he adopted a "highly aggressive stance in a sustained attack" with a hurley and there was no basis for arguing it was self-defence. A pathologist's report found the skull was fractured and it was likely a brain injury would have been caused by the "ferocity" of the blows.