A case has been registered at the Sunlight Colony police station and is being probed.
The deceased, identified as Shri Das, hailed from Gautam Budh Nagar in Uttar Pradesh and lived with his wife and three children in south Delhi's Jal Vihar.
He had been working as a sanitation worker with the South Delhi Municipal Corporation (SDMC) on contract for the past 15 years.
"After reporting to duty at a government school in Sarai Kale Khan on Friday, he went to relax in the rest house.
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He looked inside through an opening in window and found his father lying on a chair with no movement.
He raised an alarm following which police reached the spot and found Ram dead.
"There were finger print marks on the deceased's neck indicating he had been strangled to death but we are waiting for the autopsy report," said the officer.