Documentary filmmakers Julia Willoughby Nason and Michael Gasparro on their new project “American Murder: Gabby Petito,” the first docuseries on the high-profile case made with the blessing of her family. Documentary filmmakers Julia Willoughby Nason and Michael Gasparro on their new project “American Murder: Gabby Petito,” the first docuseries on the high-profile case made with the blessing of her family.