What is the ruling of the Sharia on a police officer's dealings with his criminal father: Should he apply the law to him, thereby being considered disobedient, or should he overlook his crimes of theft, assault, and harassment?

The son must advise his father and condemn his actions. If the father does not respond, the son is obligated to apply what Sharia and the law dictate by apprehending him if caught in the act of committing a crime, or by reporting him. This is not an act of disobedience but rather a form of enjoining good and forbidding evil, which is obligatory both by Sharia and by law, as Allah Almighty says: (O you who have believed, be persistently Qawwameen [firmly standing] in justice, witnesses for Allah, even if it be against yourselves or your parents and relatives. Whether one is rich or poor, Allah is more worthy of both. So follow not [personal] inclination, lest you deviate. And if you swerve or turn aside—then indeed Allah is ever, of what you do, Acquainted).