Rajesh Dessai was the brother of former Goa minister and senior BJP leader Ramrao Dessai.
"Forensic examination has revealed, he died due to consumption of poison. We are investigating whether he was fed the poison or he took it to end his life," Inspector Ravi Dessai told PTI.
"Viscera sample has been sent for forensic examination to ascertain the nature of poison," he said.
A case of unnatural death has been registered at Curchorem Police Station, the police inspector said.
Rajesh Dessai was acquitted in the murder case in 2013 and was residing in the farmhouse ever since.