It is a long and harrowing list.
Some involve a wall of silence from complicit or terrified witnesses, others involve failed prosecutions leaving more questions than answers, and some happened on foreign soil.
To see the gallery click above and to read more stories on the background of each crime click the 'buy this photo' link.
One harks back to the Victorian era.
Another is one of Britain's most notorious with allegations of police corruption and twisted detectives hampering the investigation from the inside.
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