Inside the $128 million heist that shocked the world -- and the police chase that followed

It took at least nine hard blows from an ax to smash the glass case in Dresden's historic Green Vault. Once the glass shattered, the two masked thieves grabbed 21 priceless diamond-studded artifacts and disappeared.

It was November 25, 2019, and in the space of a few short minutes, some of the world's most valuable historic jewels had vanished.

Now, the six men accused of carrying out one of the biggest jewel thefts in history are preparing to go on trial in Germany starting Friday, January 28. But the mystery of what happened to the treasures they are alleged to have stolen endures.

This is the story of a heist that stunned the world -- and the meticulous police work that led to the capture of six members of the family gang that police say are believed to be responsible for it.

Adorned with more than 4,300 diamonds, the treasures stolen from the Green Vault were worth at least 113 million euro ($128 million), according to the state prosecutor's office. However, the director of Dresden's State Art Collection, Marion Ackermann, said their material value doesn't even begin to reflect their "incalculable" historical and cultural importance.

Nearly all the stolen artifacts were made during the rule of Frederick Augustus III, the last Elector of Saxony, who was later known as Frederick Augustus I, the first King of Saxony.

They included a 1780s hat clasp decorated with 15 large and more than 100 small diamonds, as well as a 96-centimeter (38-inch) sword and a scabbard, or sheath, which together contained more than 800 diamonds.

The historic Green Vault is located inside Dresden Castle. Credit: Zoonar GmbH/Alamy Stock Photo

But it wasn't just the immense value of the loot that captured the world's attention, it was the brazenness with which the raid was allegedly carried out.

Roy Ramm, a security consultant and former commander of specialist operations at New Scotland Yard in London, told CNN that crimes like this are increasingly rare.

"Technical security has improved over the years with CCTV alarm systems and all kinds of high-tech protections, so [there is a high] risk of early detection and being actually caught in the act ... you need some inside information and a very, very detailed plan," he said.

According to investigators, four months before the robbery, a suspect went to the city of Magdeburg, 180 miles northwest of Dresden, to collect a dark blue used Audi S6: the future getaway car.

The vehicle had already been deregistered, but the police said the gang went even further in their efforts to disguise its origins, changing its color to silver and leaving only the roof dark.

A handout photo from the police shows one of the stolen pieces. Credit: Staatliche Kunstsammlungen

"What this says to me is that these people planned meticulously; they were running through, in their own minds, how the robbery would take place, and what the police reaction would be, and all the time they were thinking of ways of disrupting the police activity or giving themselves more time," Ramm said.

"If the car was seen by a bystander leaving the scene, and that person was able to give a description of the car, once the police started making inquiries into that vehicle, those inquiries would become more complicated, more difficult and more time consuming to resolve."

And police say the gang's preparations didn't stop with the getaway car.

A few days before the heist, the bars across the window where the thieves entered the vault were cut, according to authorities. Removing the metal grille completely might have raised the suspicion of passers-by, so the suspects covered their tracks by temporarily sticking the bars back in place with glue, police said.

The window was in a blind spot, so it wasn't visible on security cameras and the whole area was in "complete darkness," the Saxon State Ministry of Culture and Tourism said in response to an inquiry from the Saxon parliament. A motion sensor that should have been triggered by the theft didn't go off. The ministry said the alarm had gone off the day before the crime and security guards failed to reactivate it. CNN reached out to the state prosecutor's office for more details about the alarm failure, but the office wouldn't comment because the investigation is ongoing.