A woman in her 40s has been arrested in connection with the death of eight-year-old Anthony Ward at Charleville, Co Cork.
Gardaí investigating the death are now treating it as murder.
The woman arrived at Mallow Garda Station in an unmarked garda car at 6.15pm.
She had been arrested earlier for questioning by detectives investigating the death.
Detectives have 24 hours to question the woman and then she will have to be charged or released.
A post mortem examination on the boy's body was completed at lunchtime.
Gardaí say that for operational reasons they are not releasing the preliminary results, but it is understood they indicate that Anthony Ward died of asphyxia.
The technical examination of the Ward family home has now been completed.
Investigating gardaí were earlier granted an order in the district court extending the time for them to preserve the scene at the Cork house.