The incident took place in Kokrajhar district late Wednesday night, police said.
"Some people brutally killed three people, including an old couple, in Milanpur village," said Kokrajhar Superintendent of Police Sunil Kumar, adding that the suspects could have been from the same village.
All the three victims were aged 65-70 years, he said.
"We recovered the bodies today morning. We have detained some people," Sunil Kumar said.
About two months back, some villagers, in an inebriated condition, killed a 55-year old man in Narainpur Tea Estate in Assam's Cachar district on the suspicion that he practiced black magic.