Surendra Koli, the co-accused in the serial killings in Noida's Nithari village, has 'admitted' that he was behind the grisly murders during a narco-analysis test conducted on him, a source in the Directorate of Forensic Sciences at Gandhinagar said on Wednesday.

The source, speaking on condition of anonymity, said Koli's 'admissions' during the tests indicate he used to rape and kill children as an 'ego-satisfying habit' as he was sexually deprived and feared that he was becoming impotent.

Koli, the servant of the prime accused, businessman Moninder Singh Pandher, also said under the influence of the 'truth serum' that he saw his employer entertaining several prostitutes at his house in Noida where skeletal remains of several children were found by police last month.

DFS sources said Koli had 'admitted' to systematically chopping the bodies of the children, including minor girls, and dumping them in the drain behind Pandher's house on several occassions.

The accused made some 'admission' regarding the murder of a Noida-based sex worker Payal, whose missing cell phone led police to the skeletal remains.

Koli's narco-analysis test was conducted on January 8 by a panel of forensic experts, including psychologists, psychiatrists, anaesthetists and doctors, while Pandher's test was conducted the next day.

However, Koli's admission regarding the role of Pandher in the killings was unclear and officials were tight-lipped about this matter.