The correct answer is true.
It is true that the author of the article has a bias against John Brown.
We can clearly note the bias when the author writes " We rejoice that old BROWN has been hung. He was not only a murderer of innocent persons, but he attempted one of the greatest crimes against society—the stirring up of a servile and civil war." When an author is biasing its writing means that it tries to prejudice or pud adjectives so the reader can interpret the text in a determined way. It is not recommended to bias writing. it is the reader the one who has to have their own conclusions.