A lengthy note was discovered on the body of one of the men killed in the Kanturk shooting in Co Cork.
A detailed 12-page note was found on the body of Diarmuid O'Sullivan, the 23-year-old student found dead alongside his father in a field near the family farm on Monday.
A third and final post-mortem examination in the case was completed this afternoon, but gardaí said they would not be disclosing details of the results.
A file will now be prepared for the Director of Public Prosecutions and the coroner.
Gardaí are trying to determine the sequence of events that led to the deaths of brothers Mark and Diarmuid and their father Tadgh.
Mark was discovered in the family home, while Diarmuid and Tadgh were later found in a field 500 metres away.
All three had suffered gunshot wounds.
One line of inquiry is that the tragedy was caused by a dispute over inheritance.
Gardaí are now examining if the note can provide evidence on whether the killings were pre-planned.
Justice Minister Helen McEntee described the deaths as an "unspeakable tragedy".
Speaking on RTE's Morning Ireland, Ms McEntee also paid tribute to the emergency services who responded to the shooting.
She said: "I'm not sure what I can say other than this is an absolute tragedy. I do want to offer my sincerest condolences to the family, to the entire community who I know are in shock following on from this.
"Just to acknowledge as well, I know a lot of local services attended the scene and to thank them for the way in which they have carried out their work.
"This is an unspeakable tragedy and I really hope the family can find some solace somehow."
The bodies were taken to Cork University Hospital after state pathologist Dr Margaret Bolster attended the scene.
The Garda said post-mortem examinations on the bodies of two of the men were completed yesterday but the results were not divulged.
A Garda spokesman said yesterday evening that "contrary to some reports", there had been "no Garda interaction with the deceased men, or their family, prior to the tragic events of October 26 2020".
Gardaí have indicated they are not looking for anyone else in relation to the incident.
They were alerted to a "critical firearms incident" at around 6.30am on Monday after Tadgh O'Sullivan's wife Ann raised the alarm that firearms may have been discharged at her home.
Gardaí were told three men were in the house, and one may have suffered gunshot wounds.
The Garda initiated its critical firearms incident response, and negotiators attempted to make contact with anyone in the property during the morning.
Officers from the emergency response unit, armed support unit, national negotiator unit, technical support unit (Garda Headquarters), southern region dog unit and air support unit were involved.
Shortly after 1pm, gardaí approached the house where they found the body of one of the brothers in a bedroom.
The bodies of his brother and father were found on adjoining land after an aerial search.
A number of firearms were found at the scene and seized. They are being examined by ballistic officers.
The home remained sealed off yesterday to allow gardaí to conduct a technical examination of the house and adjoining land.