JonBenét Patricia Ramsey (August 6, 1990 – December 25, 1996) was an American child beauty pageant contestant who was discovered murdered in her home in Boulder, Colorado in 1996. The six-year-old's body was found in the basement of the family home nearly eight hours after she was reported missing. She had been struck on the head and strangled. The case, which after several grand jury hearings remains unsolved, continues to generate public and media interest.

Madeleine McCann disappeared on the evening of Thursday, 3 May 2007. She was on holiday with her parents and twin siblings in the Algarve region of Portugal. The British girl went missing from an apartment, in the central area of the resort of Praia da Luz, a few days before her fourth birthday, and has still not been found. Madeleine's parents, Kate and Gerry McCann, have said that they left the children unsupervised in a ground floor bedroom while they ate at a restaurant about 120 metres (130 yards) away.

The Zodiac Killer was a serial killer who operated in Northern California in the late 1960s and early 1970s. The killer's identity remains unknown. The Zodiac murdered victims in Benicia, Vallejo, Lake Berryessa and San Francisco between December 1968 and October 1969. Four men and three women between the ages of 16 and 29 were targeted. Numerous suspects have been named by law enforcement and amateur investigators but no conclusive evidence has surfaced. The killer originated the name "Zodiac" in a series of taunting letters sent to the local Bay Area press. These letters included four cryptograms (or ciphers). Of the four cryptograms sent, only one has been confirmed to have been decoded.