When people disappear, it is often said the hardest part for their relatives and friends is "not knowing" - the speculation over whether a loved one is alive or dead - what psychologists sometimes call the lack of "closure".
In Mexico, the war between the country's rival drug cartels has seen kidnapping and killing take place on a staggering scale.
After 6 years of violence, 24,000 people are missing - and an estimated 16,000 victims of murder remain unidentified.
The BBC's Tom Bateman reports from Mexico on the country's "disappeared".
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