The Lincoln Assassination Documents is a new book and has not yet been purchased by any OhioLINK library. Because it is still under copyright, it is not freely available on the Internet.
When you know the title of the item you are seeking, the first step is to search by title in an online catalog.
In all of these catalogs, you can use the subject heading:
Lincoln, Abraham, 1809-1865 -- Assassination
Because this has been a topic for many years, there may be books in the following databases that are full text because they are no longer copyrighted.