Cold cases, unidentified victims, and investigations that remain unresolved.
The Zodiac Killer case concerns unsolved attacks and taunting ciphers in Northern California between 1968 and 1969, one of America's most famous murder mysteries.
Jack the Ripper was the unidentified killer linked to the 1888 Whitechapel murders in London, one of history's most famous unsolved homicide cases.
The 1947 murder of Elizabeth Short in Los Angeles remains one of America's most famous unsolved homicide cases.
The Isdal Woman case centers on an unidentified woman found dead near Bergen, Norway, in 1970, one of Europe's most enduring unidentified-person mysteries.
The unsolved 2000 murder of the Miyazawa family in Setagaya, Tokyo, notable for an unusually rich forensic record, a killer who appears to have remained at the scene for hours, and enduring uncertainty over the offender's identity.
The 1991 murders of four teenage girls at an Austin yogurt shop remain one of the most notorious and disputed homicide cases in Texas history.