Using the Twitter API and a language like Python you can scrape data on a user’s profile or tweets v easily, Google Twitter api developer guide and it’ll show you all the fields available.
You could write a script that looked for every @handle, name, or bio or tweet that contained an array of keywords (slurs, genocides, etc) to make this list. The full research probably discloses the methodology with that list, but it’s limited by it as not everyone who is an awful account has the name hitler88lover.