CrPC vs BN Act: Pollock vs Maganbhai Case

Bhai, koi meri help kar sakta hai? Main confuse hoon isme. CrPC (Code of Criminal Procedure) section 156(3) ke under FIR lodge karna, aur BN Act (Banerjee vs Commissioner of Police) mein 'duty of police to investigate' ka kya fayda hai?

Mujhe lagta hai ki dono hi police ko investigate karna chahte hain, lekin kya exact difference hai? Kya CrPC ki FIR lodge karne wali baat aur BN Act ki police ko investigate karna chahte wali baat kisi cheez se alag hai? Koi explain kare? Pls!