Andrzez Piolunowicz had been found seriously injured in the apartment in Killarney town centre on Sunday and was taken to Kerry University Hospital in Tralee.
However on Tuesday, after his condition deteriorated and because of the nature of his injuries, he was transferred from Kerry University Hospital to Cork University Hospital. He died on Thursday night.
Supt Flor Murphy of Killarney gardaí said while gardaí were not seeking anyone else in connection with the deaths, both deaths — that of the father and baby Karol Rozycki — are being investigated.
“There are two deaths now and they will be fully investigated. The investigation will continue to determine the full facts and the full circumstances surrounding the incident,” Supt Murphy said.
An incident room had been set up in the garda station which is just opposite the Park Place apartment complex where the family lived for some months.
Statements have been taken from a number of people in the apartments. Work colleagues and friends are also being interviewed.
A garda liaison officer, separate to the liaison officer who helped the child’s mother, has been appointed to help the family of Mr Piolunowicz. Two sisters of Mr Piolunowicz live in Kerry.
Both women had attended the special memorial Mass which was attended by around 500 people from both the Polish and Irish communities in St Mary’s Cathedral on Tuesday afternoon to pray for baby Karol and his mother Anna Rozycka.
They have also met with Ms Rozycka.
Mr Piolunowicz worked at the Aghadoe Heights Hotel, in the accommodation section. His partner and mother of the child Anna Rozycka worked as a chef at the hotel. Both were well liked.
Fr Piotr Delimat, the chaplain to the Polish community in Killarney, seconded from the Archdiocese of Krakow, said the deaths were “a tragedy for both families”. He said Anna was “amazed” at the help she received in Killarney and has taken some of the candles left at her door to place on the baby’s grave in southern Poland.
The help from the gardaí, the interpreters and the Irish media in general who kept a “respectful” distance in terms of the contents of the reports and dealing with the family was greatly appreciated, the priest also said.
Mr Piolunowicz had been looking after baby Karol on Sunday and Ms Rozycki raised the alarm when she returned from work at around 6pm and found the apartment very quiet and the bedroom door locked.
Suspecting something was wrong, she raised the alarm and a friend helped to break down the door of the bedroom.
It is understood the incident at the apartment had occurred only a short time before she arrived.
Paramedics tried to revive the infant.
Baby Karol will be buried tomorrow after 2.30pm Mass of the Angels at the church of St Martin in Ochaby in the Krakow regions of the southern part of Poland. Ochaby lies around 20km north-west of Bielsko-Biala.
Ms Rozycka has also thanked Aer Lingus and the Killarney undertakers O’Sheas who met the expenses of the repatriation.