What are the main themes of The Devil and Mr. Casement by Jordan Goodman?

This book is about Roger Casement, the Irish-born member of the British Foreign office who investigated King Leopold II of Belgium's horrific actions in the Congo. Casement traveled about the Congo and interviewed people, which led to the release of the Casement Report. The Casement Report revealed Leopold had enslaved or killed millions of local people. His report led Leopold to give up the Congo as his personal domain. The Devil and Mr. Casement is about Casement's attempts to reveal the horrors Peruvian Julio César Arana committed in the Putumayo region of the Amazon against the local Indians, as Arana killed hundreds of thousands of locals in an attempt to extract rubber. The British Parliament investigated Arana's Peruvian Amazon Company, based in London, but Arana was left unpunished and continued to conduct abuses in the Amazon. 

One of the themes of The Devil and Mr. Casement is the difficulty of cracking down on abuses, even abuses as serious and extensive as those in the Putumayo region. While Casement arrives in the region with optimism that his investigation will end the abuses, "Casement's confidence soon dissolved into frustration and despair" (164). His attempts to arrest the perpetrators of the abuse in the region are unsuccessful because the political authorities in the region back Arana.

Another theme in this book is the flawed nature of justice. Arana, the perpetrator of great abuse, goes unpunished, while Casement, the humanitarian (who was also knighted), is soon afterward executed by Britain for helping Germany attempt to foment Irish independence from the British. The ways in which these two men are treated by the British justice system reveals the unfairness present in the British justice system at the time.