Assam Chief Minister Himanta Biswa Sarma said that a magistrate was arrested for "compromising his responsibility" in a case of sexual assault and murder of a 13-year-old girl in Darrang district.

The victim girl, who was working as a domestic help, was found dead in the house of her employer in June.

Besides the main accused who is a Sashastra Seema Bal (SSB) personnel, several other government employees the then superintendent of police, an additional SP, the officer in charge of the police station concerned and three doctors were already arrested in the case.

Addressing a press conference here, the chief minister appreciated the Criminal Investigation Department (CID) for conducting the investigation in a highly professional and scientific manner.

"The magistrate was arrested today. The CID has already arrested the SP, Additional SP (of the district), the OC of Dhula police station and three doctors who had conducted the first post-mortem examination," he said on Friday.

Additional DGP (CID) A Y V Krishna said that the arrested government officials did not follow the norms and gave false reports to close the case as an incident of suicide.

The CID, which formed a special investigation team (SIT) to probe into the case, had on Thursday stated that Ashirvad Hazarika, the local magistrate, was absconding.

Sarma, who also holds the home portfolio, said that this case was very significant in the history of Assam Police as a fresh probe was started as per his instruction more than a month after the victim's last rites were performed.

"This is a rare case in which the body was exhumed and a second post-mortem examination was conducted. We were lucky that the victim was a Christian girl and her body was buried. The way the CID collected forensic and scientific evidence, the entire probe gave a new dimension to the investigation process in Assam Police," he said.

The chief minister lamented that the probe exposed a nexus involving the then SP, ASP, OC, magistrate and government doctors.

On Thursday, the suspended SP Raj Mohan Ray was arrested for allegedly taking Rs 2 lakh as a bribe to dilute the case, CID had said.

Ray had received the money through the then Officer-in-Charge of Dhula police station Utpal Borah who was arrested by the CID on October 31.

The rape and murder case led to outrage in the state. The chief minister visited the girl's family on August 12 following their allegations that the police displayed extreme dereliction of duty in collecting evidence.

The additional DGP (CID) told reporters that a detailed probe and evidence have established the accused men's offences of molestation, murder, destruction of evidence and attempt to rape under several sections of the IPC and POCSO Act.

"It was not a case of death by hanging. The accused hit hard on the girl's head and neck, and then strangulated her with a coconut coir rope after she threatened to tell his wife about the sexual assault," the officer said.

He also said that the CID consulted forensic experts and conducted DNA profiling of the main accused and it matched with the semen found on the undergarment of the victim.

In a detailed presentation, Krishna showed how the agency proceeded to unearth the case.