Why was Lincoln murdered?

Possibly one of the first books that proposed a major conspiracy behind Lincoln's assassination. His theory was that Stanton, LaFayette Baker, and Pinkerton all played major roles in the conspiracy and that all 3 aided and abetted Booth. According to Eisenschiml, Stanton was the main plotter, among Stanton's reasons were Lincoln's too forgiving attitude towards the South. While the book lacked hard evidence that would definitely incriminate Stanton there were, like the JFK assassination, an endless number of intriguing and suggestive coincidences and circumstantial evidence.