In Nightcrawler, Jake Gyllenhaal plays a freelance cameraman who races to the sound of police scanners, looking for shots of auto crashes and shootings — hopefully including victims with bloody wounds. It’s appropriate that the film is debuting tonight on Halloween. Nightcrawler is a horror story about the grotesque preoccupation with crime and violence on TV news in Los Angeles. But the writer-director, Dan Gilroy, says its implications are broader than that.