當一樁謀殺案沒有目擊證人、線索甚至連屍體都找不到的時候，調查員的調查過程勢必艱難萬分。首先要先想辦法蒐集並分析所有證據，但如果最後這些證據無法指向鎖定的嫌犯那也是徒勞無功。多數的被害者都是被認識的人所殺，這也是為什麼他殺案件是最簡單易解的案件。但是英國的他殺案件卻有20%被歸類為「未知情況」。在這個系列當中，羅比寇特蘭將揭露八起英國警方偵辦過最艱難、最複雜也最令人頭痛的謀殺案件。每一集節目的重點就是關鍵證據：證據是怎麼被發現的，這項證據有什麼意義，而它又為何成為破案關鍵。從和許多首次公開說明案件的負責案件的調查員對談，還有和法醫學專家對談中，羅比將揭曉最驚人的轉折點和比虛構更不真實的真實案例。這是一系列紀錄警探手法之藝術的影片，警探們運用辦案技巧與決心去解決看似不可能破解的案子，因為失敗和成功的一線之隔就是關鍵證據。
When there’s a murder with no suspect, no leads and perhaps not even a body, that’s when investigators face their toughest test. Evidence must be gathered. Evidence must be analysed. But evidence is worthless if it can’t be pinned to a suspect... Most murder victims knew the person that killed them. That's why homicide, in many cases, is a straightforward crime to solve. Yet 20% of UK homicides are classified as “circumstances unknown”. In this series, Robbie Coltrane reveals eight of the hardest, most complex and baffling murder cases ever to be investigated by British police. The focus of each programme is the trail of evidence: how it was discovered, what it meant and how it became critical to crack the case. With interviews from the lead investigators and forensic specialists, many speaking for the first time, Robbie reveals the astonishing twists and turns of often stranger-than-fiction cases. It is a record of the detectives’ art: using skill and determination to solve seemingly unsolvable cases – because the only difference between success and failure is critical evidence.
