6pm on 31st January 2017, three days after Chinese New Year. 64-year-old Hang Yin Leung hears a knock at the door. She’s alone at home and not expecting any visitors. Her husband works 7 days a week at the takeaway business they’ve built together. She answers the door and within seconds, the lives of this hard-working family are changed forever.

A violent attack by six men leaves the house ransacked. They are heard laughing as they run off down the road with bags of stolen goods and the family savings. But the worst is yet to come… as Hang Yin reveals to police the true nature of the attack, she falls ill and is rushed to hospital. She never recovers.

Her death launches a huge cross-border manhunt and one of “the most difficult homicides” the detectives have ever investigated. Shot over 12 months, this compelling film interweaves extraordinary access to Thames Valley Police with an intimate portrait of a British Chinese family coming to terms with the true impact of murder. Alongside the real-time police investigation unfolds the rarely-told story of migrants from Hong Kong who came to the UK in search of a better life for their son. A universal tale of hopes and dreams, shattered by an unprovoked attack. An unexpected twist brings the film to its powerful conclusion.

Full programme information: http://www.channel4.com/info/press/programme-information/catching-a-killer-a-knock-at-the-door

Catching a Killer: A knock at the door will air on Monday 14 May at 9pm on Channel 4.