The arrests were made yesterday, eleven days after the highly decomposed body of the old woman, identified as Kumari Sahu, was recovered at Dadi village under Tikabali area on August 24, they said.
Sniffer dogs and scientific team were pressed into service during investigation following recovery of the body and subsequently one Ranjeet Sahu, an auto driver, his wife Mamata Nayak and mother-in-law, were nabbed, they said.
The main accused Sahu in association with other two had killed the old woman, who was their neighbour, to grab her gold ornaments, Monarama Mallick, Inspector In-Charge of Tikabali police station, said.
After the incident, a report was lodged with Tikabali police by the son of the deceased on August 22 saying Kumari Sahu was missing August 21, sources said.