Filmmaker Matthew Heineman spent nearly a year in Mexico for his newest project. There, he embedded in an area ravaged by gang-related violence with a vigilante group working to stop a murderous drug cartel. Heineman’s film, “Cartel Land” has just received a prestigious George Polk Award for documentary film. The director joins “CBS This Morning: Saturday” to discuss how he gained access to the group and the dangerous challenges he faced while filming. Source