When Prince died in 2016, he left behind a treasure trove of unreleased material — thousands of songs in various degrees of completion were tucked away in a locked vault at his Paisley Park estate.

There was just one problem: Nobody knew the combination to the safe, not even Prince when he was alive. He had reportedly forgotten the code several years before his death and left the vault locked.

With no way in, the assistance of experts was required to open the vault following his death in 2016, which is where Dave McOmie, a professional safecracker based in Oregon, came into the picture. He already knew the exact model of Prince's vault - a Mosler American Century - when Prince's estate reached out to him. "I keep track of these things - just my job, really," McOmie noted on an episode of This American Life, saying he had seen a photo of the vault online. At six and a half feet tall, several feet wide and 6,000 pounds, it's not easily cracked into. "No burglar has ever defeated a Mosler American Century, not once, ever."

McOmie turned to a common safecracking technique: microdrilling. A small hole is drilled through the door in a precise location so as to view the combination lock from the inside using a periscope. Based on its configuration, McOmie could then determine the correct code to open the door. But first he'd need to avoid triggering what's known as a "mousetrap relocker," a device placed in many high-security safes. "Basically, if the vault senses it's being tampered with," McOmie explained, "a spring-loaded mechanism fires like a mousetrap, snapping this metal block into place, that physically makes it so the door can't open, even if you have the combination."

Two drill bits, one carefully evaded mousetrap relocker and several hours of drilling later, McOmie was able to peer inside with his periscope and examine the combination. "I could see each of the four little tumblers, they looked like little grindstones, turning this way and that," he said. "It was a beautiful sight to see." From there, he dialed the correct code and opened the door. "Everybody clapped. I was a little embarrassed. When the door came open, the archivist looked inside before I did. I've just been trained, through decades of doing this, not to look."

Inside the expansive vault was precisely what Prince's estate — and fans around the world — had imagined: stacks upon stacks of unreleased recorded material. "I don't know the exact dimension, but approximately 20 feet by 40 feet," McOmie said. "Now, by bank standards, that is on the large side. And yet there was hardly any room in the vault, because it was just jam-packed with these industrial shelving units, and every one of them was packed bottom to top with tapes."

In the fall of 2017, the vault was relocated to a facility in Hollywood by Comerica Bank & Trust, the executors of Prince's estate. A few months later, a judge denied a request filed by Prince's siblings, heirs to the estate, to have the vault moved from southern California in fear of nearby wildfires.

This past summer Prince's shelved 2010 studio album Welcome 2 America was released - one of the unreleased finds located inside the vault. There's likely much more to come. It's estimated that the tapes found in the vault contain approximately 8,000 unreleased songs, which the Prince estate is currently organizing and evaluating for future posthumous releases.

25 Times Prince Crossed Paths With Rock's Biggest Stars

Ask a musician if they've got a Prince story to tell and they just might surprise you.