Passport block

I need your valuable suggestion where one of my close associate's mother is missing since last 7 months. He is NRI & working in abroad. His family along with his mother is residing in India from last 10 yrs. In the month of Oct his mother has left home without intimating anyone & the same was witnessed in Cc camara on police verification. He rushed from his work place to India immediately after knowing this incident & started searching. But they could not find her from certain location as the CC camaras were not working & could not locate her even thorough search from their family members. They even telecast in TV's & pasted Palm plates. They even received calls from the people who have witnessed his mother in near by temples but their efforts were in vein when they have approached that places. Meanwhile his married sister came from her village & lodge a complaint against her brother & sister in law on her mother's missing. Local police have also filed the FIR based on her complaint though he has visiting the local PS regularly and upgrading on search progress. After 1.5 months he flies back to his work place as he got an emergency call from his company. Now he again wish to come back to India on a holiday & wants to search his mother. My query is 1.what is the best possible way to find her mother ? 2. If he come to India again, is there any possibility of asking his passport to be surrendered by his relatives or police?