In the weeks before their deaths, Tadg O'Sullivan and his youngest son had plenty of time to nurse the grievance that had consumed them for months.
The 59-year-old mechanic and his youngest son, Diarmuid (23), had been alone at the homestead in north Cork for a fortnight.
His wife Anne O'Sullivan (60), who is ill, had gone to Dublin to have surgery, accompanied by the couple's eldest son, Mark (26), and on their return, both stayed at a friend's house to allow her recuperate, rather than return to a household simmering with tension.
Gardaí investigating the murder-suicide that engulfed the townland of Assolas, near Kanturk, last week suspect that father and son may have used this time to hatch a plan of astounding cruelty.
According to informed sources, gardaí are investigating whether Tadg O'Sullivan may have coaxed his wife and eldest son to return home last Sunday, assuring her that things would be better.
So last Sunday, Anne and Mark returned to the traditional farm cottage where the family had lived for more than 30 years. She was probably weary of the tension and rows, said one local who knows the family. Seriously ill, she had decided to settle her affairs and left her farm, her inheritance from a father and an uncle, to her eldest in her will.
She and her eldest had been personae non gratae in the O'Sullivan household for months. She had been staying at a friend's house outside the village since she returned from a hospital stay in Dublin, accompanied as she often was by her protective oldest boy.
According to one local source, "they came back, through some form of promise or coaxing", he said.
Friends had been worried about Anne. One person was so concerned about the anger directed towards her they made discreet enquiries with gardaí on her behalf. Sources close to the investigation confirmed that advice had been sought by a "third party", and there was no formal complaint, no statement from an injured party and so no formal investigation could take place.
By last Sunday evening, the O'Sullivan family was home together. Only those present know what transpired in the household overnight and three of those are dead.
What is evident is that as Anne and Mark slept, either Tadg or Diarmuid, or both, prepared the ground for a murder that gardaí suspect they may have been plotting for days, if not weeks.
Some time that night, one of them went down the avenue to the big half gates to the property - usually kept open - and locked them together.
The house phone had been smashed. The mobile phones belonging to Diarmuid and Tadg had also been broken up. They were later found discarded in the house.
At 6.40am on Monday morning, father and son stood at Mark's bedroom door and one or other, or both, opened fire on him.
Anne awoke to carnage, and according to sources witnessed her husband and her son at Mark's bedroom door, armed with rifles. She fled in her night clothes and without her shoes on, but with her mobile phone. Diarmuid pursued her outside and destroyed it, but did not try to stop his mother from escaping, sources said. She ran down to laneway, only to find her escape blocked by locked gates.
She ran across the fields to the nearest house more than a mile away. Distraught and frantic, it took her 20 minutes to reach the safety of her nearest neighbour. She told them Tadg and Diarmuid had shot Mark and were now barricaded inside the house.
The 999 call to the emergency services was logged at 7am.
Daylight broke as the Garda helicopter touched down in the GAA pitch at Castlemagner. The instruction had been dispatched up the line before first light: two armed men, father and son, barricaded inside a farmhouse in the Kanturk countryside. One son dead, a mother who escaped with her life.
A dozen gardaí in uniform and detectives in plain clothes assembled on the narrow country road leading to an isolated, one-storey farmhouse.
Gardaí surveyed the terrain: the long, gated avenue to the house, surrounding fields, some thick forest, a river and miles of rolling countryside.
All presented potential escape routes. They knew the men were armed - three weapons were licensed to the household - and locals had reported to gardaí they had heard two gunshots, but could not specify the time.
In a neighbouring house, Anne, trembling and in shock, divulged the horror she had just witnessed. Gardaí gently coaxed from her what details they could about the crime scene and her husband and youngest son, whom she believed to be barricaded inside. Negotiators trained in talking down siege situations would need as much detail as they could about the men they were trying to reach.
By 7.30am, an inner cordon of gardaí had taken up positions surrounding the house and an outer cordon amassed along the roads and laneways.
Over the course of the morning, the Emergency Response Units and the armed support unit from Cork joined the cordon, and specialist paramedics were airlifted to the scene from Cork.
Over the next five hours, the specialist teams assembled outside the house tried to establish 'proof of life'. The vehicles associated with the family were still in the yard, which led to suspicions that Tadg and Diarmuid may still be inside. Negotiators used a loudhailer calling out the names of Tadg and Diarmuid. The phones either didn't ring or rang out.
By 1pm, still unsure as to what to expect on the other side of the front door, the emergency response team led the way inside. The front door to the house was closed but not locked. There was little sign of disturbance until they reached the bedroom and discovered the body of Mark O'Sullivan lying on his bed. It was clear he had been shot multiple times.
Forty minutes later, a Garda helicopter sweeping the surrounding farmlands detected the bodies of two people close to a ditch and near a ring fort.
The bodies of Tadg and Diarmuid lay several feet from one another, two .22 rifles on the ground nearby. Both father and son died of single gunshot wounds to the head but gardaí are relying on the results of ballistics and forensic tests to establish the choreography of their deaths. According to one local man, two shots were heard to ring out simultaneously.
A lengthy letter - a suicide note effectively - was reportedly strapped to Diarmuid's thigh. No spur-of-the-moment eruption of anger tipped Tadg and Diarmuid over the edge. This was premeditated murder, planned and executed with brutal precision.
The letter outlined over 12 dense pages is said to outline Diarmuid's unhappiness at his mother's decision to exclude him from her will. But the letter also indicated that he did not intend to kill her. One source close to the inquiry said had they wanted to, they could have. The fact that she would have to live with the aftermath of what he had done was a crueller punishment than death.
The land that caused such grief is 115 acres, some of it set in good tillage. According to local lore, Anne's father and uncle bought it together many years ago and sub-divided neatly among themselves.
Anne inherited both plots from her father and her uncle, restoring the original farm to one.
Neither Anne nor Tadg worked the land. For the best part of 30 years, it was leased out to neighbouring farmers, earning a decent annual income. Farms of that size can generate up to €20,000 to €30,000 a year.
Tadg had a smaller holding of his own in Roskeen, a village between Kanturk and Mallow, where he was from. He earned his living as a mechanic at Greenhall Motors in Buttevant.
Anne worked as nurse in Mount Alvernia Nursing Home in Mallow. She is outgoing and threw herself into community events, according to locals. She often fundraised for local causes. Tadg, quieter than she was, was involved in the GAA, as were their sons.
According to one local politician, there are several schools in the region and all are noted for producing high-achieving students. "Education is seen as a way out of the bad land," he said.
The sons of Anne and Tadg were both high achievers. Mark and Diarmuid both attended the local national school, Ballyhass, and secondary school at Coláiste Treasa in Kanturk. Both boys worked their way through college.
Diarmuid had a Saturday job in a hardware shop in Kanturk. Mark worked in Teach Altra nursing home all through college until 2018 when he was studying for his Masters. He had graduated from University of Limerick with a business and law degree and moved on to do a Masters at University College Cork.
Mark's Facebook page is a vibrant testament to a full life. The photos he posted from his Erasmus year at university in Thessaloniki in Greece are liked and commented on by friends all over the world.
He gave back, too. In his fourth year of law at University of Limerick, he volunteered to "buddy" students from overseas universities on their Erasmus year. One of them was Marina Barone, then a final-year law student in the University of Bologna, who called him an "angel" who showed her the ropes during her stint at the college.
Diarmuid was quieter, more studious and less outgoing than his older brother, local people said. He had just finished a four-year accountancy course at Cork Institute of Technology in June and was due to be conferred with a First Class Honours degree in the coming weeks.
Dr Dan Collins, head of student affairs at CIT, said staff at the department of accounting and information systems described him as "a young man with promise, who was a hard worker, respected, and held in high regard by staff and students alike".
The day he graduated from UCC last spring, Mark is photographed with a parent on either side - his mother, Anne resting her hand on his arm and his father, Tadg, hands clasped in front, a broad smile on his face, a picture of parental pride. Within a year, the lives of all three in that photograph had changed utterly.
Anne had developed a medical condition, a recurrence of an old illness, and was seriously unwell. Perhaps that put her in mind of settling her affairs. She had arranged to bequeath her land to Mark, to the frustration of her husband and youngest son, Garda sources say. Anne's reasons were her own. Resentment festered, enveloping Diarmuid and then his father, Tadg, who sided with him.
Both sides resorted to law. The brothers had been "communicating by solicitor's letter for months", according to one neighbour. But few people in the locality - other than Anne's close friends - knew about the simmering tensions or the intensity of feeling building in Diarmuid and his father.
And it was beyond comprehension that it should lead to their grotesque decision that they would settle the dispute with annihilation.
"It is almost inconceivable to contemplate in any depth as to how two people acting in concert, one being highly intelligent, the other leading a life without blemish, did what they did," said a source.
Gardaí investigating the suspected murder-suicide expect to present files to the coroner outlining the facts of the tragedy for inquests into their deaths. Legal correspondence recovered from the house attests to the bitterness of the inheritance feud.
Detectives are tracing back the movements of Diarmuid and Tadg in the days before the murder, who they were in contact with, how long their plan had been in train.
Details of the suicide note have not been disclosed, but according to Garda sources, as well as attempting to justify the catastrophic action and funeral preferences, it confirms that father and son acted in unison. A second note left by Tadg is understood to be shorter.
Both were intended for Anne, who will receive them when she is ready.
Neil Websdale, professor of criminology at North Arizona University, has studied hundreds of familicides - the phenomenon in which perpetrators kill their families and often themselves.
Familicide is rare, he said, and it is mostly perpetrated by men. Cases often share common features: the "potential emasculation of males, the shame, the humiliation, the ebbing of power and control".
There may be patterns but seldom explanations.
"Ultimately we are in the haunting presence of the inexplicable," he said.
That sense of incomprehension was echoed at the funeral service for Tadg and Diarmuid on Friday.
Anne O'Sullivan may never learn why her husband and son ripped her entire world from her. But she found the strength to attend their funeral service and burials, side by side, at the cemetery beside St Mary's Church in Castlemagner.
Yesterday, she said goodbye to her son, Mark, who was laid to rest far away from his brother and his father, at the cemetery beside the Church of the Immaculate Conception in Kanturk.