ON A rainy morning in December 1968, a police motorcyclist screeched to a halt in front of a cash-laden Tokyo bank vehicle and ordered four men to get out, warning it was about to explode.

Seconds after the cop ducked underneath the car, plumes of smoke began billowing up and he screamed at them to flee.

"It's dynamite. It's going to blow!" he yelled, sending the terrified men running for their lives.

Then he calmly climbed behind the wheel and drove off with 300 million yen, never to be seen again.

It was Japan's biggest-ever cash heist, netting the crook the equivalent of $3.4 million today, and leaving a mystery that remains unsolved 44 years later, having eluded some of Japan's top investigative minds.

The huge police probe cost over $12 million and involved hundreds of detectives - two of whom died of exhaustion working on the case - who questioned a staggering 118,000 people.

Decades later the crime continues to captivate the nation, having spawned books, movies, TV dramas and a comic book series.

Many older Japanese still remember what they were doing when they heard of the audacious theft, the anniversary of which falls on Monday.

"Wasn't that really bold? People in the old days were so naive they believed anyone dressed like a police officer," said Keiji Harashima, 53, the manager of a trucking company office near the scene.

The Japan of 1968 was brimming with energy after hosting the Olympics in Tokyo four years earlier. Its red-hot economy was running full tilt and factories were pumping out cars and consumer electronics.

On December 10, four unarmed employees of the Nippon Trust Bank were delivering year-end bonuses and other monies totalling 294,307,500 yen to a Toshiba plant in a quiet Tokyo suburb.

They were just 200 metres from the factory when the police motorcycle overtook them, outside the walls of Japan's biggest prison.

The rider, wearing a police uniform and sitting astride a white Yamaha, told the men there had been an explosion at a branch manager's home.

Days earlier, their own manager had received a bomb threat in the mail.

"We have been informed your car may be wired with dynamite," the counterfeit cop said as he crawled underneath the vehicle.

Investigators said the smoke that the men saw was actually a harmless flare, but it was enough to send them running for cover, giving the robber plenty of time to make his getaway.

The motorcycle he left behind was a fake, a stolen bike painted to look like the real thing.

At some point the outlaw switched to a Toyota - also stolen - that was found abandoned four months later, along with the metal boxes that once contained the huge cash haul.

The 19-year-old son of a real local motorcycle policeman emerged as the chief suspect, but just five days after the robbery he was dead, having swallowed potassium cyanide that his father had bought.

The man insisted on his son's innocence and there was no clear evidence to implicate the boy, despite his being the leader of a local youth gang.

A 26-year-old man, a skilled driver who was working at a Canadian government office in Tokyo, was arrested a year later because he resembled a composite portrait of the robber.

His alibis checked out and he was released without charge.

The statute of limitations ran out after seven years and one of Japan's biggest ever police investigations was folded up.

Although the cash heist record has since been rewritten - it is now held by a $7.4 million sting on a Tokyo security company last year - the "300 Million Yen Robbery" lives on in the popular imagination.



Originally published as Heist remains unsolved, 44 years on