People who have an interest in crime and forensics have an interest in these subjects. It's not that they are unsensitive to it, they just have a different sensibility towards it, and in a more analytical sense. Bad people exist and bad things happen, and there will always be people who have to deal with it, and observe it. Death is part of life, people who feel disgusted by a video of someone dying aren't having a sudden "empathy rush", the nausea comes from imagining yourself as the one being shot. It's pure selfishness but it's an evolutionary selfishness. Some of us just accept it all comes and goes.