A court in Kerala has acquitted four persons accused of raping two siblings and driving the girls to commit suicide, leaving the state government with a legal challenge amid allegations of deliberate lapses in the investigation and prosecution.

The Congress, the main opposition, and the BJP staged massive protests before the Palakkad police chief’s office on Monday following Friday’s acquittals of three of the suspects.

One of the four accused — who had all faced serious charges under the Protection of Children from Sexual Offences (Pocso) Act and for abetment of suicide — had been acquitted on September 30.

A fifth accused — a minor — is being tried in a juvenile justice court.

The Opposition has demanded a CBI probe.

The sisters — one 11 and the other 9 — were found dead 52 days apart in January and March 2017 at their shanty home in Walayar, an industrial town in Palakkad district.

Both are said to have killed themselves, unable to bear the torment.

The incident had rocked the state with the ruling Left Democratic Front government facing severe criticism as some local CPM leaders had openly supported some of the accused.

The children had been repeatedly abused over a period of time and medical reports confirmed they had been subjected to unnatural sex.

The additional sessions court in Palakkad — the designated Pocso court — had handled the case involving the four adults. The juvenile was tried at the chief judicial magistrate’s court, the designated court for such cases.

After a trial that lasted more than a year, the additional sessions court had on Friday acquitted V. Madhu, M. Madhu and Shibu, saying the prosecution and investigating officers had failed to present clinching evidence against the accused.

Pradeep Kumar, the fourth adult accused, was cleared on September 30 for the same reasons.

While Kumar was released last week, those acquitted on Friday will be released once prison authorities get a copy of the court’s order.

The juvenile — who cannot be named — is in custody at a correction centre for minors.

V. Madhu and M. Madhu are both related to the children’s mother. Shibu worked with the victims’ father, a casual labourer, and stayed with the family for a few years. Pradeep and the juvenile were neighbours of the Dalit victims.

The elder of the victims was found dead, hanging inside their one-room house in January 2017. Her sibling’s body was found hanging at the same spot 52 days later.

Police had then said that even the second child was sexually abused and the repeated torment led them to commit suicide.

The girls’ parents had said in their statement that V. Madhu sexually abused their elder daughter but fear of going to the police had made them let him off with a warning not to enter the house again.

The couple have a son, who is now in Class X and who has since been admitted to an orphanage by the Child Welfare Committee because of the atmosphere at home.

The opposition on Monday stalled Assembly proceedings and demanded a CBI investigation but chief minister Pinarayi Vijayan was non-committal.

“The verdict has gone against our expectation,” the CPM leader said but added: “We will decide on whether to re-open the case or hand it over to the CBI after examining the verdict.”

Leader of the Opposition Ramesh Chennithala said the chief minister’s statement was very disappointing. “We always get shocked when we hear about heinous crimes in north Indian states.... These crimes did not happen in Uttar Pradesh or Chambal, but in Kerala that we believe is progressive and cultured,” the Congress leader said. “It is shameful that this government and the prosecution helped the accused and not the victims.”

Chennithala said it was a shame that only 16.7 per cent of Pocso cases end in convictions in Kerala.

“In 2013, 1,583 Pocso cases were registered in Kerala. That number doubled to 3,178 in 2018,” he told the Assembly.