BRUSSELS (AP) — Nearly a decade after a brazen diamond heist at Brussels airport, it looks like a near-perfect crime.

While one person was convicted and sentenced to five years in prison and a small part of the loot — estimated in 2013 to be worth $50 million — was recovered, 18 other people were acquitted in 2018 and four more were acquitted on appeal Wednesday, leaving it unclear whether the mastermind will ever be found.

The Brussels appeals court said in its ruling that “the elements of the investigation are not sufficiently reliable” and that they were insufficient to convict the last four defendants in the case.

The robbery drew comparisons to the Hollywood movie “Ocean’s Eleven” for its clean, clinical execution that left no one hurt.

On a crisp, wintry evening in 2013, eight robbers dressed in police clothing cut through security fences at Brussels international airport and headed for a Swiss-bound plane where parcels of gems from the nearby Antwerp global diamond hub were being loaded. They brandished machine guns at pilots and transport security officials, got into the hold of the plane and took off with 120 parcels.

It barely took five minutes and none of the 29 passengers on the plane knew anything was happening. Because of the perfection of the operation, there were immediate suspicions there was help from inside the airport.

Investigators thought they were close to finding the robbers several times, especially three months later when they detained several dozen people in a three-nation sweep and recovered some of the diamonds. But the courts found the evidence unconvincing.

“There were so many elements that were presented as overwhelming evidence, but after a close look appeared to be deformed, and badly interpreted,” said defense lawyer Benjamine Bovy, adding that the those looking into the case were too fixed on one scenario only.

“The mountain gave birth to a mouse,” Bovy said.