TV tonight: the search for the murderer of Northern Irish journalist Lyra McKee

A documentary series gains impressive access to the detectives who have been hunting for the killer since 2019. Plus: Mark Gatiss returns as a bookish postwar sleuth. Here’s what to watch this evening

9pm, Channel 4
The 2019 murder of the journalist Lyra McKee in Derry was a grim reminder that, while the Troubles are in abeyance, it’s still a stretch to describe them as being over. Filmed across seven years, this three-part documentary gains impressive access to the detectives hunting for Lyra’s killer. It’s intense and gripping: the team struggle to persuade any witnesses (there were more than 150) to come forward and gradually realise that they are, in fact, investigating the leadership of the New IRA. Phil Harrison