History's Greatest Mysteries Season 4

In a perfectly planned robbery, thieves steal half a billion dollars in masterpieces from the Gardner Museum in Boston; it's been three decades since the brazen heist, and an exhaustive search has failed to recover the stolen goods.

It's one of the most infamous crimes in American history: the gruesome murder of a young beauty, unsolved for decades. There's a long line of suspects, each more mysterious than the next. Can the questions surrounding one of history's most notorious unsolved cases finally be answered?

During World War II, Japan plunders a fortune worth hundreds of billions of dollars from occupied countries, but to this day its whereabouts are unknown.

The history books say Adolf Hitler committed suicide in the final days of World War II, but not everyone believes there's sufficient proof; questions have swirled for decades about his possible escape.

In July 1996, one of the worst aviation disasters in American history leaves 230 people dead and countless questions unanswered; it's a tragedy that changes the aviation industry forever.

She was the last pharaoh of Egypt and one of the most famous queens of all time, but her death in 31 B.C. has been shrouded in mystery. Cleopatra's body and final resting place have been lost without a trace for over 2,000 years, leaving the world's top archaeologists baffled. Can new evidence finally uncover Cleopatra's missing tomb?

They've been called the world's greatest archaeological enigma. 2,000-year-old geoglyphs made in the Peruvian desert that span over 50 miles. The drawings are so massive, they can only be seen from the air. Can new research finally unravel their secrets? What is the true purpose of the incredible Nazca Lines?

In 2016 a mysterious illness strikes dozens of government officials in Cuba. Over the next few years, hundreds more are afflicted. But investigations raise more questions than answers about this bizarre epidemic. What is the true cause of the strange phenomenon known as "Havana Syndrome?"

It is a legendary ancient city, said to be overflowing with gold. For centuries, explorers put their lives on the line searching for it. As the endless quest to uncover this infamous city continues, will anyone ever find it?

It's one of the most famous prehistoric monuments on Earth -- a mysterious arrangement of stones that have adorned the English countryside for millennia; nobody knows how the landmark was built or why.

Thousands of people swear they've encountered the legendary North American creature Bigfoot, but Bigfoot has never been officially identified; as evidence continues to mount, and photos are scrutinized, the mystery endures.

It's the only unsolved air piracy case in history; in 1971, a man hijacks a Northwest Orient Airlines flight, demanding four parachutes and $200,000; he jumps out of the plane with the money and is never seen again.

It's one of the most famous stories from the Bible; for thousands of years the tale of Noah's Ark is shared, but little is known about what happened to the ark.

A look at what could cause mysterious vanishings in the Bermuda Triangle, a 500,000 square mile area of the Atlantic where ships, planes and unsuspecting travelers have been lost without a trace.

During World War Two, the Nazis stole vast amounts of art, gold, silver and currency, and stashed it across Europe; while some of the plunder has been recovered, much more is still missing nearly 80 years later.

Awe-inspiring and mysterious, the pyramids of Egypt are significant wonders of the ancient world; more than 4,000 years old, they are celebrated architectural marvels, but no one fully understands how they were built or why.

An ancient mechanical device found on a 2,000-year-old shipwreck has become known as the world's first computer. The machine is centuries more advanced than historians thought possible, but its origin and true purpose are shrouded in secrecy. Can modern technology finally unveil what the mysterious Antikythera Mechanism actually is?

One of history's most notorious pirates, Blackbeard, is said to have had a treasure worth millions of dollars. After centuries of searching, the legendary hoard remains missing. As new evidence is unearthed, the mystery endures: what became of Blackbeard's lost treasure?

In 1930, a New York Supreme Court justice with close ties to Tammany Hall, and future president Franklin Delano Roosevelt, steps out of a steakhouse and disappears. For decades, the politically charged case dominates mainstream media and remains unsolved nearly 100 years later. But could a deathbed confession finally tell us what really happened to the notorious Judge Joseph Crater?

One of the holiest and most powerful relics from the Bible has been missing for over 2,000 years. While some believe the Ark of the Covenant was destroyed, many people think it's still out there. Could new clues finally tell us what happened to the Ark, and lead us to where it can be found?

In 1997, thousands of people in Phoenix witnessed strange lights; this could be an UFO sighting.

In 1587, a group of settlers land off the coast of North Carolina on Roanoke Island to establish the first English Colony in America. But only a few years later, the 115 men, women and children seemingly vanish without a trace, leaving only cryptic clues. The search to find out their fate has endured for over 400 years. Can new technology finally tell us what happened to the Lost Colony of Roanoke?

On November 22, 1963, President John F Kennedy is assassinated, shaking the nation to its core; while an initial suspect is captured, many believe there's more to the story; investigators and amateur sleuths alike have been searching for answers.

In 1969, one of history's most elusive serial killers terrorizes Northern California. He taunts investigators with cryptic ciphers and clues, leaving police and the public questioning his identity for over 50 years. Can new evidence and technology finally crack his code? Who is the Zodiac Killer?

Despite centuries of sightings and searches, one of the most infamous deep-sea monsters remains unidentified. As evidence continues to mount, the mystery endures: does the Loch Ness Monster really exist? And if so, what could it be?