Murder of the Lowe family
On 5 August 2000, 26-year-old taxi driver Azhar Ali Mehmood started a fire at the Telford home of 16-year-old Lucy Lowe, with whom he had been engaging in illegal sexual activity since she was 14. The fire killed her and her unborn child, her 17-year-old disabled sister Sarah, and her 49-year-old mother Eileen Linda.
Source: Wikipedia — Murder of the Lowe family (CC BY-SA 4.0)