What’s a UK crime that remains unsolved to this day?

The Daily Mirror recently published a list of 1,000 unsolved murders going back decades. However, there are apparently officially 2,500 unsolved murders in the whole of the UK going back to the 1940s. The true number is invariably a lot higher. Different police forces count their oldest unsolved crimes, e.g. Suffolk Police count their oldest unsolved murder as 11-year old Linda Smith in 1961. However, there are older crimes than this (e.g. the murder of Heather Abbott at Mildenhall in 1952). On the other hand Merseyside police counted up to 169 unsolved murders. When I looked some of these up on the British Newspaper Archive, some were tragic cases where someone had murdered someone & then taken their own life. So technically those crimes remained unsolved. Also what is counted in the stats appears to have changed. I've seen older lists of unsolved crimes & they sometimes counted the victims of hit & run accidents. I don't think that is done today. It wasn't unusual for a driver in a fatal accident in the past to be charged with manslaughter. Occasionally inquest juries found the victims of botched abortions were murdered. Finally, there are a lot of open verdicts. Often someone had died from an overdose but they couldn't determine intent, so an open verdict was often returned. However, some cases were highly suspicious but it was difficult to prove that the person was harmed by someone else. So it is hard to work out how many unsolved murders there are in the UK. But this is thrown into sharp relief by the number of cold cases in the US, an estimated 250,000 since 1980.