A wealthy Indian businessman and his servant have been sentenced to death for the kidnap, rape and murder of a 20-year-old woman. It is the latest development in the Nithari serial killings story, which has gripped India for over a decade.

Moninder Singh Pandher and his groundskeeper Surinder Koli were found guilty of the 2006 killing of domestic worker Pinki Sarkar, The Indian Times Reports.

The murders and ensuing trials are the subject of a US documentary, The Karma Killings, which aired on Netflix.

Filmmaker Ram Devineni told the BBC that he is convinced of Pandher's innocence: "With his beard and moustache, he looked like the perfect Bollywood villain," Devineni said. "Mr Pandher was a rich man, he was this privileged person and everyone wanted to bring him down."

The case against the pair began when police found the remains of 15 people, including Sarkar and children, in the sewers outside Pandher's residence.

Prosecutors said Sarkar was abducted by Koli while walking past Pandher's mansion on the way home from work.

The groundsman had previously confessed to killing and raping children as young as three – though he has since retracted this confession.

Both he and his employer have been at the centre of allegations regarding the deaths of as many as 40 women and children, in Nithari, a village in Noida, bordering New Dehli.

The murders appear to have taken place inside the grounds of Pandher's lavish property, dubbed the "house of horrors", in 2005 and 2006.

Prior to the recent trial, servant Koli was already sentenced to death after being found guilty of five murders.

Pandher was a free man, having been sentenced to death for one of the murders in 2009, only to win an appeal at a high court.

He now faces the death penalty again after being found guilty, along with Koli in the present trial. He faces four further murder charges while his servant faces nine more.

Pandher's lawyer said his client would appeal against Monday's verdict in a higher court.

Nithari Noida killings
The Indian Central Bureau of Investigation (CBI) conduct a search operation at a drain, outside the residence Moninder Singh Pander in January 2007 in Noida STRDEL/AFP/Getty Images