One of the most moving documentaries that I have watched is called "Blackfish". This documentary is on Netflix and it follows the events that surrounding the supposedly dangerous killer whale: Tilikum. 

Tilikum was captured off of Iceland's coast in 1983 and was raised almost completely in captivity. The documentary argues that it is this history that resulted in his unpredictably threatening nature during his life. The event that the documentary culminates in is the 2010 attack by Tilikum towards his trainer - Dawn Brancheau. Brancheau's demise was heavily publicized and SeaWorld, the group in question over its stance on keeping whales in captivity, claimed that this occured due to Brancheau wearing her hair in a ponytail rather than a braid, which would have confused Tilikum. 

Through the interviews from ex-SeaWorld and SeaLand employees, it is understood that Tilikum was one of the friendliest whales, who has a close bond with Dawn. But, he also did have a history of unpredictably dangerous behavior, having attacked previously two of his trainers. Many nueroscientists relate this unstable mentality to him being captured as a baby. Being raised in captivity and attacked ruthlessly by other whales who were larger and stronger caused him to have behavioral developmental changes that can be attributed to him lashing out unexpectedly at people that he would normally be gentle and playful. 

From this movie, I learned the dark side of animal entertainment like SeaWorld. It is a very sad documentary, but I strongly recommend it to learn more about the development of animals in captivity and the emotional depth of the killer whales, who are not actually that dangerous when they are free. 

Hope you enjoy watching it.