Muckraker

Noun

1. One who investigates and exposes issues of corruption that often violate widely held values; e.g. one who exposes political corruption or the poor conditions in prisons.
2. One of a group of American investigative reporters, novelists and critics of the Progressive Era (the 1890s to the 1920s).
3. A sensationalist, scandalmongering journalist, one who is not driven by any social principles.