A chilling documentary reveals how investigators tracked a murderer’s online activities. Plus: a rousing biography of Sir Alex Ferguson. Here’s what to watch this evening

10pm, Channel 4
“If there’s narcissism, they’re going to post things.” This chilling two-part documentary from the US tells the wild story of Todd Kohlhepp, a serial killer whose Amazon reviews foreshadowed the crimes he committed. It begins with Kala Brown, a woman who had been missing for two months, being found chained inside a container on Kohlhepp’s property – using a chain lock connected to his online review of padlocks. This triggered the unravelling of what had Kohlhepp had been doing online and in real life before then. Hollie Richardson