The found footage ending was a happy accident. While filming the final scenes for the film, on the last day of principal photography, the camera died. Not having enough time to re-charge the camera's battery, and lacking the footage needed for the film's ending, the director came up with the idea to end the film from an onlooker's perspective, filming with a smart phone.
The film was heavily inspired by the violent revenge/exploitation films of the 70's and 80's, featuring synth music and old school camera techniques.