If you want to find out who owns the rights to a TV show or movie, how do you go about doing it?
Copy it and see who sues.
Also, according to their FAQ page: “If you are not certain about the ownership or have other related questions, you may wish to request that the Copyright Office conduct a search of its records for a fee of $75 per hour. Additional information can be found in Circular 22.”
Assume that anything first published in the U.S. from 1964 onward (except by the federal government) is still under copyright. Assume that anything first published in the U.S. before 1923 is out of copyright and in the public domain. Assume that you better do your research on anything first published in the U.S. 1923-1963.