The deceased, identified as Abdul Hamid Ansari used to stay alone in Madanpura area of Nagpada, they said.
As a daily routine Abdul's grandson Wahid used to visit his house every morning. However, when he reached the house this morning, Wahid found his grandfather lying motionless on the floor with his hands and legs tied, police said.
According to police, the assailant had tried to break open the cupboard, where Rs 6.25 lakh were kept, though he was unsuccessful. They suspect that robbery could be a motive behind the crime.
Police have registered a case under sections 302 (murder), 394 (voluntarily causing hurt in committing robbery), 397 (robbery) and 452 (house-trespass after preparation for hurt, assault or wrongful restraint) of the Indian Penal Code against the unknown accused.
Post-mortem report is awaited and further investigation is on, police said.