In a major breakthrough, the CBI has arrested a 23-year-old “serial rape offender” allegedly involved in brutal rape and murder of an engineering student on December 16, 2016, in Ranchi.Rahul Rai, who carries many pseudonyms like Ankit, Aryan and others, was picked up by the CBI from a Uttar Pradesh jail where he was cooling his heels in other rape cases. After committing the gory crime in Ranchi, Rahul reportedly fled to Lucknow where he committed three rape crimes in a similar manner.The Ranchi’s Nirbhaya was raped and murdered at her house. The perpetrators had burnt her after committing the crime.The incident occurred on the fourth anniversary of the gory gang rape and murder of a paramedical student in New Delhi and had rocked the state which witnessed widespread protests, rallies and candle marches demanding immediate arrest of culprits.The CBI’s Lucknow special crime branch on Saturday produced Rahul before a Ranchi court which forwarded him in judicial custody till July 6.The court of special judicial magistrate (CBI) Ajay Kumar Gudia is yet to decide on the CBI’s request, seeking Rahul on police remand for interrogation. Earlier, the case was investigated by the Ranchi police and the crime investigation department (CID) but no breakthrough was made. The police had conducted DNA tests on more than 80 suspects in this case but all reports didn’t match with the victim’s DNA. Cyber experts had also been engaged to search and examine social media, including mails, but they too failed to find any clue.The state government on January 3, 2017, had finally recommended for a CBI probe. A year later, the Centre approved the government’s request leading to registration of FIR by the CBI on March 28, 2018.The semi-naked half-charred body of the victim was found inside her house. The incident came to light after the girl’s sister, failing to reach her on phone, sent some neighbours to check on her. On reaching the house, they found the door ajar and smoke emanating from the room.When they entered, they found her body lying near the bed with her face fully burnt. Other materials in the room were also gutted.The premiere investigating agency registered the FIR against unknown persons under Sections 448 (house trespass), 302 (murder), 201 (causing disappearance of evidence of offence), 328 (causing hurt by means of poison), 376 (rape) and other sections of the Indian Penal Code. CBI’s deputy superintendent of police (DSP) RS Solanki was entrusted with the investigation of the case.