I don't have the correct answer, but with this situation getting worse day by day i think Bihar police will get involved with this soon.
& After listening to this news that Mumbai police is not allowing the IPS officer from Patna to enter the city who was suppose to investigate the case. the Indian public has already declared that Mumbai Police is involved with this so called Bollywood Mafia.
Another news is from Rhea Chakraborty, that she just left her house the same day she uploaded a video saying "Satyamev Jayte, The truth shall prevail". and also the Mumbai police mentioned that they are not able to contact her and her family. where as her lawyer refuted Bihar Polices claim that she was "missing", and said till date she has not received any summons from them in connection with the case of actor-friend Sushant Singh Rajput's death.