The police arrested three persons - Valiya Madhu, Kutti Madhu and Pradeep Kumar - accused of rape and murder of two minor girls in Walayar on Tuesday.
All the three were left on bail later. Fourth accused Shibu is still at large.
The police action came a day after Kerala High Court ordered their arrests based on an appeal by the state government.
The government challenged the aquittal of the four accused by the POCSO (Protection of Children from Sexual Offences) court in Palakkad.
The death of two minor girls in 2017 in a space of 52 days had created a lot of uproar in the state. But the POCSO court acquitted all the accused for want of evidence.
In its appeal, the government had said the lower court verdict was "absolutely perverse and wholly unsustainable."
The government sought a direction to call for the records of the case, set aside the sessions court judgement and convict the accused for the offences or order an investigation into the crime.
The government had admitted that the police had failed to conduct a foolproof investigation touching upon all areas which should have been covered.