10 Strangest Unsolved American Mysteries

2. The Black Dahlia

In January 1947, Elizabeth Short was gruesomely murdered. Her body was found mutilated, sliced in half at the waist, in Leimert Park in Los Angeles. The media quickly publicized the story, giving her the nickname "The Black Dahlia."

Short's murder remains unsolved to this day, and is still the source of widespread speculation. Movies have been made and James Ellroy wrote a bestseller about it. But despite all the attention paid to this case, it was never solved. It's quite possible the murderer was a man connected to other killings who served life in prison. Or the man could still be walking the streets today. Nobody knows.

3. The Murder of JonBenet Ramsey

On Christmas Day in 1996, American child beauty contestant JonBenet Ramsey was murdered in her home in Boulder, Colo. The 6-year-old's body was found beaten and strangled in the basement of the family home just eight hours after she was reported missing.

Initially, her parents and brother were the prime suspects, but they were partially exonerated in 2003 thanks to DNA testing supporting that they were not involved. Her parents were completely cleared in 2008.

In August 2006, John Mark Karr (still in the running for biggest creep of all time) confessed to killing Ramsey while he was being held on child pornography charges. However, Karr's DNA did not match that found on JonBenet's body, and he was not charged. The Boulder Police Department has been overseeing the reopened investigation since 2009.

4. The Orphanage Mayday Mystery

On every May 1 since 1981, a cryptic ad has been placed by a group calling itself The Orphanage in the University of Arizona's student newspaper, the Arizona Daily Wildcat. Typically appearing as a mix of languages, symbols and mathematical equations, the ads have a few recurring themes.

The Orphanage, the secret society supposedly behind the ads, is offering "The Prize" which is an unidentified reward for whoever solves the mystery. White Rabbit/Wonder Bread are unknown items transported by The Orphanage, and images of Martin Luther appear often. If you're confused, well, so are we.

A rumor has circulated for years that an eccentric lawyer named Robert Truman Hungerford, who claims to be the legal counsel for the secret organization, is actually the madman behind all of it. It has never been proven, though.

5. Max Headroom Broadcast Signal Intrusion

We all have heard some pretty awesome Internet hacking stories, but what about a TV signal takeover? In 1987, on the evening of November 22, an unknown hijacker was successful in interrupting two television stations within three hours. The first signal intrusion occurred on WGN-TV's "Nine O'Clock News" during the sports segment, when a person broke in for about 30 seconds wearing a Max Headroom mask (Max Headroom is a British artificial intelligence character). There was no audio, just a buzzing sound as the person stood in front of a swaying piece of metal.

However, just a couple hours later, during the broadcast of "Doctor Who" on the PBS station WTTW, the signal was hijacked using the same video that was shown during the WGN intrusion. This time, though, the person in the mask appeared with distorted audio and was on screen for a much longer time, ultimately mooning the camera and getting his butt smacked with a flyswatter by an unknown accomplice. To this day, nobody knows who is responsible.

Check out the full video of the hijacking here.

6. The Toxic Lady

On the evening of February 19, 1994, 31-year-old Gloria Ramirez was admitted to the Riverside General Hospital's emergency room in Riverside, Calif. She was suffering from the effects of advanced cervical cancer. Shortly after being admitted, Ramirez passed out.

When hospital staff began trying to defibrillate her heart, several people noticed an oily sheen covering her body, and a garlic-like odor in the room. When a nurse attempted to draw blood, she noticed the smell of ammonia coming from the tube, and a doctor nearby saw manila-colored particles floating in the blood.

The nurse fainted, and the doctor, Julie Gorchynski, became very sick. Ramirez died as many of the staff began falling ill. Her body was moved into isolation and the ER was evacuated. All in all, 23 people became ill, five were hospitalized, and one nurse was kept in the hospital for 10 days with tremors and apnea. Gorchynski was the most seriously affected, having to stay in intensive care for two weeks, contracting apnea, hepatitis, pancreatitis, and necrosis of the bone marrow which crippled her legs and required at least three surgeries.

So what caused all this? After tests and analysis done by a hazardous materials team, the coroner, and the Ramirez family's pathologist, the final diagnosis was that she simply died of cervical cancer and wasn't toxic at all. A possible explanation is that some toxic reaction took place inside Ramirez's body and gave off a poisonous gas that affected the staff. Another is that the ER victims suffered from a mass sociogenic illness, triggered by the frightening unknown odor. In other words, their illnesses weren't real. But that is very hard to believe.

7. The Zodiac Killer

In the late 1960s and early 1970s, the serial killer operated in Northern California, claiming 37 murders in letters to local papers, although investigators agree on only seven victims (two of which survived).

The killer originated the name "Zodiac" in a series of taunting letters sent to the local Bay Area press. These letters included four cryptograms, only one of which has been solved. Several suspects have been named in the killings, and several more people have come forward claiming to know who the killer is, but the case has remained open by the California Department of Justice since 1969.

8. Bird Deaths in Arkansas

On the last two New Year's Eves, in the city of Beebe, Ark., hundreds of blackbirds have fallen from the sky and died. On New Year's Eve, 2010, an estimated 5,000 birds were found dead on the ground, and this past New Year's Eve at least 100 birds fell from the sky before midnight.

Scientists blamed fireworks for the first mass bird death, saying they were spooked from their roosts by the explosions and began flying into homes, buildings, telephone poles and each other. No such explanation was given for the most recent deaths. Scientists will say that mass in-air bird deaths are common, but to happen in the same small city on the same night two years in a row seems a little too coincidental to us. And if this was so common, why doesn't it happen in more towns across America?

9. The Disappearance of Jimmy Hoffa

Perhaps the most famous "union man" ever, Jimmy Hoffa was last seen in late July 1975, at a restaurant in suburban Detroit. He was declared legally dead on July 30, 1982. However, his body has never been found, and years of FBI investigations have not been able to conclusively determine Hoffa's fate. It is widely assumed, though, that he was killed by members of the Mafia.