Explanation:

- Efficiency refers to the speed and cost-effectiveness of the criminal justice system, but it does not guarantee fair and impartial treatment.

- Decisions (courts) indicate the judgments made by judicial bodies, focusing more on the outcomes rather than the process itself.

- Fairness involves equitable treatment but is not a specific constitutional guarantee.

- Due Process is the correct option. It is the constitutional guarantee ensuring that all legal proceedings are conducted fairly and without bias, protecting individual rights.