public domain movies

I'm sorry if this is not the right place to post but I have an idea there are some b-movies I like and according to a web site they are in public domain. So my idea is to write my own version of the movie. But one how do I know if the site is right and if it is in pd can the people who made the movie sue me any way

 

There's a list of US public domain films on Wikipedia, and other places.

What do you mean by 'write my own version'?

 

I mean write my own virsion. Write a book based off the movie do a retelling of the story and make it better

 

Anything before 1923 you ought to be safe in the U.S. After that, its going to take some research.