The interrogators told him that he should confess to the killings and seek forgiveness, otherwise he and his family would suffer badly, the officer said.
This disturbed him, and he confessed to three more killings, the officer said.
When contacted, Superintendent of Police Rahul Lodha did not specify exactly which psychological ploy the sleuths were using to make Khamra speak.
"We are trying everything on him to extract every piece of information," Lodha said.
"We told him he should repent and confess to his crimes or he will suffer for his sins for long," the SP said.
"Our psychological treatment is working wonders. We are expecting him to confess to more murders," the SP added.
Khamra is resident of Madideep in Raisen district of Madhya Pradesh. Jaikaran Prajapati (30), a local resident and Tukaram Banjara (48) who hails from Yavatmal in Maharashtra were his alleged accomplices.
Prajapati and Banjara allegedly told poice that the gang had killed 33 persons -- drivers and cleaners -- in 23 incidents of truck robbery since 2010.
Khamra killed his victims saying he was "liberating" them, the duo allegedly told police.
The gang operated in Madhya Pradesh, Chhattisgarh, Maharashtra and Odisha, police said.
"They befriended truck drivers on highways. The gang leader would throw a party for them, during which drinks laced with sedatives would be offered. Once the drivers and cleaners fell asleep, they were killed," said Jaideep Prasad, Bhopal Range Inspector General of Police.
The bodies of victims would be dumped in remote places and the goods in the trucks would be sold off. The trucks were dismantled and disposed of in parts, police said.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)