A woman in her 30s was being questioned last night after being arrested in connection with the death of toddler Santina Cawley.
The woman, who is not related to the tragic two-year-old, was arrested at an address in Cork yesterday morning and taken to Gurranabraher Garda Station.
She can be held under Section 4 of the Criminal Justice Act 1984 for an initial period of 12 hours, which can be extended.
The arrest came as gardai continued their murder probe into the child's death.
Santina was discovered critically injured in the Elderwood Park flats complex just off Cork's Boreenmanna Road early on Friday.
A neighbour had contacted gardai after a man called to his flat screaming for help and saying his daughter was badly injured.
The child's mother, who lives at an address in a different part of Cork, was not present at the time.
Santina was treated at the scene by paramedics at 5.30am before being taken to Cork University Hospital. She died a short time later.
Gardai upgraded their investigation to a murder probe on Saturday after a post-mortem examination by Assistant State Pathologist Dr Margaret Bolster revealed Santina had met a violent death.
The toddler had suffered numerous injuries to her head, neck and body, including multiple bone fractures.
Officers have not released the full results of the post-mortem examination for operational reasons.
However, detectives believe the injuries are consistent with the toddler having been subjected to a sustained, vicious beating.
The arrest followed a massive garda operation which involves up to 30 personnel, including forensic experts.
Two properties at the flats complex were sealed off by gardai for forensic tests, along with a vehicle found parked off the Boreenmanna Road.
Statements were taken from a number of people resident or present at the Elderwood flats complex on Thursday and Friday, including Santina's father and his girlfriend, who is not the child's mother.
It is understood that a party had been taking place at one of the flats in the complex on Thursday evening.
Gardai have again appealed for anyone who was at the flats complex between 6pm on Thursday and 6am on Friday and who has not yet spoken to them to come forward.
Santina's body remains at Cork University Hospital and is not expected to be released back to her family for another 48 hours.
Tributes have flooded in for the little girl from relatives, neighbours and family friends.
Santina was hailed as "a little angel" who brightened the lives of many.
The heartbroken uncle of the toddler took to social media to express his horror at her loss.
"RIP beautiful angel. Cruel world. Live life to the full and have no regrets," he wrote.
A photo of Santina showed the toddler drinking from her bottle from the back seat of a car.
Dozens of other mourners also paid their respects on social media.
"My heart is broken, I can't believe what has happened," said one family friend.
"I am so sorry from my heart and soul.
"May she rest in peace, God bless her and her family."