The bodies of four unidentified murder victims were found beaten, decomposed and stuffed inside trash bags in 1985 and 2011 in Bear Brook State Park in New Hampshire. Authorities still have no clue on what the names of the victims are or who killed them.

From 1979 to 1989, a man murdered at least 10 people and raped more than 50 women in Southern California. Years after the crime, the man would call some of his victims, saying something like "Merry Christmas, it's me again!" before hanging up. The police still do not know who he is.

After being reported missing several weeks earlier, the body of Canadian student Elisa Lam was found in the water tank of Los Angeles based Hotel Cecil. Employees found her body after guests complained of problems with the water supply.

In 1959, nine hikers died of mysterious circumstances in the Ural Mountains. Evidence showed that they'd torn their tents from the inside out. And here's another odd bit of evidence: their bodies showed no signs of struggle when they were found facedown in the snow.

In 1981, Keddie, California, was hit with a tragedy when three members of the Sharp family and one family friend were bludgeoned to death with hammers, while one was stabbed repeatedly, and each body was tied with medical wrap. No arrests have been made almost 35 years later.

It has been almost 60 years since a 4- to 6-year-old boy's naked, battered body was found in a cardboard box in Philadelphia. Known as "America's Unknown Child," his identity still hasn't been confirmed, and his case is still open.

It was Christmas Eve 1945 in West Virginia when five of nine children of the Sodder family disappeared after their home went up in flames. Their remains still haven't been found decades later.

Way back in March 1922, six inhabitants of Hinterkaifeck farm in Germany were murdered with a pickaxe. And you guessed it, the case has not been solved.

The body parts of Fred and Edwina Rogers were found inside their refrigerator, wrapped neatly on the shelves in 1965. Charles Rogers, their son, is believed to have committed the crime, but he hasn't been seen since.

Kyllikki Saari, a 17-year-old from Finland, was found dead in a bog in 1953 after she was bicycling home from a prayer meeting. There were suspects including a priest and an individual who spent time in a mental hospital, but the case has still not been solved.

You probably don't want to hitchhike near that highway because from 1969 to 2011, at least 18 women either were murdered or disappeared along Highway 16 in British Columbia while hitchhiking. While a link to one killer was found in 2012, police believe they won't ever find all of the suspects.

Or axewoman, because police still don't know who committed murders from May 1918 to October 1919, in Louisiana and Texas. Many of these victims were killed by an axe, some belonging to the victims themselves. Police still don't know if the killer was a male or female, while some believe it was a supernatural force.

Where is Amy Lynn Bradley? In 1998, while on a cruise ship, Bradley disappeared after stepping out of her cabin early in the morning for a cigarette. A witness claimed to have seen her in a restroom in Barbados in 2005, but Bradley has not been seen since 1998.

The year was 1948 in Adelaide, South Australia, when an unidentified man was found dead on a beach. A piece of paper with the phrase tamán shud, which means "ended" or "finished" in Persian, was found in his pocket. An unknown poison was also found in his body.

Madeleine McCann's case continues to capture the world, as the little girl has been missing since 2007 when she disappeared from a hotel room in Portugal while her parents dined next door. The case is still open, as her parents still believe she is alive.