Season 1 Sky Mix , 2017 Watch now Season 2 Sky Witness , 2018 Watch now Season 3 Sky Crime , 2019 - 2020 Watch now Season 4 Sky Crime , 2020 Watch now Season 5 Sky Crime , 2021 Watch now Season 6 Sky Crime , 2021 Watch now Season 7 Sky Crime , 2022 - 2023 Watch now Season 8 Sky Crime , 2023 - 2024 Watch now Season 9 Sky Crime , 2025 Watch now Returning for series 9, World's Most Evil Killers will examine some of the most dangerous and prolific murderers in the world, uncovering what drove them to commit such heinous crimes.