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At the beginning of November, an advert appeared on the lost and found section of a well-known website. Amongst the pictures of misplaced iPads, recovered wedding rings and lost drones, was a photo of a smiling young man, holding a new-born baby. 'Father and partner missing', it said.

Zack's in his late 20s. He has been diagnosed with bipolar disorder. On medication, he has it mostly under control. He and his girlfriend Kirsty had just moved into a new flat and become proud parents of their first child together. Life, they thought, was good.

But one day in early November, on their five year anniversary and when the baby was just 5 weeks old, Zack left for work and never came home.

Producer: Georgia Catt.