Validity of will written on white paper

my wife's grandfather has left his last will/testament on a piece of white paper for the three fixed deposits in nationalised bank but the will is not witnessed by anyone, is this will valid, is witness for a secret will compulsory. he might thought if he witnessed his will he might face life threat by beneficiaries or so, please reply 1) Can testator's granddaughter's husband can witness the will. 2) Is there any alternative to validate the will if no one has witnessed it.