Even though the main characters in the film are tracking a giant crocodile named, "Gustave", it's only half of the story. The genocide going on in Africa(where the story takes place) left many dead bodies near the river which gave Gustave an overabundant food supply. The warlord spearheading the killings calls himself, "Little Gustave" (after the crocodile) and the majority of the movie's plot is devoted to the attacks of Little Gustave's thugs and the tribulations of the African people.
This movie is NOT about an independent serial killer, as the original TV commercials led many people to believe.