On April 20, 2006, a twenty-six-year-old woman from Paivalike village near Manjeshwar, in Kerala's Kasaragod district, came to Mangaluru with a relative to meet the man who had asked to marry her. He called himself Sudhakar and said he worked for an insurance firm. The relative last saw her boarding a bus with him. He took her to a lodge in Madikeri, raped her, and the next morning made her take cyanide tablets, then went back to Mangaluru the same morning and pledged her gold. Her murder came to light only after his arrest three and a half years later. His real name was Mohan Kumar Vivekanand, and the Indian press calls him Cyanide Mohan.
He was born in Karnataka in 1963 and from 1980 to 2003 was a physical education teacher in government primary schools in Dakshina Kannada. He has also been accused of bank loan frauds and forgery. His targets were young women of about twenty-two to thirty-five whose families could not pay a dowry or who had not found husbands, and he offered to marry them without one, under false names including Ananda, Bhaskar, Shashidhar, Sudhakar and Sudhakar Acharya of the forest department. After sleeping with each woman he handed her a pill that he said would prevent pregnancy. It was laced with cyanide. He took her jewelry and left. By the reckoning of the prosecution he killed twenty women between 2003 and 2009.
In 2009 the police in Dakshina Kannada were looking into the disappearance of a twenty-two-year-old woman, Anitha, from Bantwal taluk. Her phone records showed she had been in contact with another missing woman, and the police traced the man who was using that woman's phone. On October 21, 2009, they arrested Mohan Kumar, and found eight cyanide tablets, four mobile phones and Anitha's jewelry. They charged him with her rape and murder and reopened the cases of seventeen missing women.
The cases were tried one at a time before the sessions courts at Mangaluru, with Kumar appearing by video link from Hindalga Central Prison in Belagavi. In December 2013 he was convicted of raping and murdering three women, Anitha, Leelavathi of Venur village in Beltangadi taluk, and Sunanda, and sentenced to death in each case. In 2017 a division bench of the Karnataka High Court, Justices Ravi Malimath and John Michael Cunha, set aside the death sentences for Anitha and Leelavathi, in one case substituting imprisonment for life without remission and in the other life with five years of rigorous imprisonment. It upheld the death sentence for Sunanda. He had lured her with the promise of a job and marriage under the name Shashidhar, taken her to Mysuru, and given her cyanide at the KSRTC bus stand there on February 11, 2008, before leaving with her jewelry.
The convictions kept coming, before the sixth additional district and sessions judge, Sayeedunnisa. In July 2019, after forty-one witnesses, she sentenced him to imprisonment until his last breath for the Manjeshwar woman, his seventeenth case. In September 2019 he was convicted of killing a thirty-three-year-old music teacher from Uppala in Kasaragod district, whom he had introduced himself to as Sudhakar Acharya of the forest department and raped at a lodge in Bengaluru in May 2007 before giving her the capsule. On October 24, 2019, the judge sentenced him to death for the 2005 rape and murder of an anganwadi worker, with ten years for abduction and seven for rape, which The Hindu counted as his fourth death sentence. In 2020 he was convicted of raping and murdering a twenty-five-year-old woman from Kasaragod, his twentieth murder conviction. The prosecution said he had used the same method in all twenty cases. Figures of thirty or more victims circulate in some coverage; the charges and convictions number twenty.
The case has been drawn on for the 2023 series Dahaad and for two 2025 films, Bhagwat Chapter One: Raakshas and the Malayalam film Kalamkaaval.