Sobhraj (78) served more than 18 years in prison after being convicted for the murder of two American tourists in 1975.
He was released on grounds of advanced age and health.
Sobhraj a French national, is suspected of killing more than 20 Western backpackers on the “hippie trail” through Asia, usually by drugging their food or drink in the course of robbing them.
He was dubbed the “bikini killer” and “The Serpent”, for his evasion of police and use of disguises.
He was suspected of many more murders, including in Thailand, where police say he allegedly drugged and killed six women in the 1970s, some of whom turned up dead on a beach near the resort of Pattaya. His true number of victims is unknown.
He was jailed in India for poisoning a group of French tourists in New Delhi in 1976, before he could stand trial on the charges against him in Thailand.
Sobhraj escaped from Tihar jail in 1986 after drugging prison guards with cookies and cakes laced with sleeping pills. Police nabbed him days later in Goa. He was jailed in India until 1997 when he returned to France.
He resurfaced in Nepal in 2003, and was put on trial for the murder of the American tourists, and subsequently convicted and jailed.