It’s not grammar, it is the use of the word “gotten” that shows that the writer is deficient in the use of the language. If one were to use “gotten” in a high school or college term paper, their grade would be marked down a few points, if not failed.
In addition, the writer claims that Manson is a mass-murderer and even thT is incorrect in every sense of the term.
Are you by any chance British rather than American?