What should I declare a minor in?

Of the choices you listed, I would probably choose pre-law. However, it might not make much difference. Choose whatever interests you most. If you want to become a police detective, you must first become a police officer. Requirements to become a police officer and how you become a detective varies depending on the police department. Most police departments that require or prefer applicants to have college don't require any particular field of study. If you want to become a federal criminal investigator or special agent, I would consider choosing accounting, computer science, a foreign language, or law as your major. Whatever you choose, make the most of your time and money while in college. Get the highest grade point average that you can, participate in a couple extracurricular activities, get a good internship, do some regular volunteer work, don't do anything illegal, and maintain a good reputation. Getting law enforcement officer jobs is becoming more and more competitive. Do whatever you can to make yourself the best candidate that you can. Best of luck!

Psychology or Social Work. Will allow you to understand the thinking of criminals and victims better.