In a big city like Philadelphia, it's easy for an unsolved murder to slip into the cold files and be forgotten. But in this case, one victim's boyfriend was set on doing everything possible to make sure people didn't forget, and that police didn't stop investigating.

After nearly two decades of silence, a man known as the Smoky Mountain Gypsy comes forward with information that could lead police to solve not one, but two different murders, which had never before been connected.

In an ocean-side town in California, a woman is strangled to death in her home and her head is wrapped in duct tape. Police are at a loss for evidence, but there is one eye-witness: the victim's four-year-old son.

In the spring of 1969, Jane Mixer becomes one of several young women murdered around the University of Michigan. Police think there may be a serial killer, but does Jane fit the pattern? And years later, how does the DNA of a 4-year-old end up found on Jane's body?

After a mother hears about allegations that her physically abusive boyfriend has sexually abused her daughter, she goes mysteriously missing for over a decade. A trunk, a storage unit, and a Cold Case detective's dogged determination help solve the mystery.

In 1991, an eight-year-old boy is kidnapped from home while his mother is at church. Police believe the kidnapper is someone close to the family, but rule out all the obvious suspects. Despite years going by, ransom notes, and briefcase full of cash, and the lack of a body keep the mother's hope alive.

In a town most famous for the death of legendary gunfighter Wild Bill Hickok, police try to solve a murder not in the 1880s, but the 1980s. This murder involves a man named David Crockett, another named "Outlaw," a bus full of hippies, and a very large rock.

Police in Columbus, Ohio spend more than a decade hunting a man who terrorized a neighborhood known as Linden. In the process, he became one of the most prolific rapists in U.S. history.

In 1993, Charles Murray, an experienced hunter, went missing on the first day of bow hunting season. His family fears that something terrible had happened were quickly realized. But who was it that found Charles out in the middle of the woods? And why did this hunter become someone else's prey?

This week marks the 71st anniversary of one of the most infamous cold cases in America - the gruesome murder of Los Angeles actress Elizabeth Short, more commonly known as The Black Dahlia. We'll go explore what makes this case so complicated, unpack the prevailing theories, and find out why some people say it will never be solved - while other claim it already is.