The son of Sandra Rivett believes he has found her murderer. Plus: the new series of cosy crime drama Shetland. Here’s what to watch this evening

9pm, BBC Two
When he was 11, Neil Berriman discovered his birth mother was Sandra Rivett – the nanny murdered in Lord Lucan’s home in 1974. Lucan vanished that night and was legally declared dead in 1999. But Berriman, now a builder, believes he has found him – and this riveting three-part documentary follows his journey as he attempts to solve the mystery. Hollie Richardson