Channel 4 broadcasts the start of a three-part documentary tonight examining the seven-year hunt for the killer of journalist Lyra McKee, who was shot dead in Derry in 2019. The case remains a stark illustration that, despite the Troubles being formally over, related violence and paramilitary influence persist in Northern Ireland, with detectives ultimately finding themselves probing the leadership of the New IRA.

Filmed over seven years, the series gains notable access to the investigating detectives as they struggle to persuade witnesses to come forward, despite more than 150 people reportedly present at the scene. Other picks in tonight's TV guide include Mark Gatiss returning as bookish 1946-set sleuth Gabriel Book on U&Alibi, Ben Miller's criminologist drama on ITV1, a documentary on the unsolved 1991 disappearance of Nicola Payne, a Sky Documentaries film on Greenpeace's 1985 anti-nuclear campaign, and Chris Morris's 2019 satire The Day Shall Come on Film4.