“We were about to catch them red-handed,” said Raluca Botea, the chief prosecutor in a special Romanian unit responsible for fighting organized crime and the leader of the hunt for the art thieves. She was one of numerous people close to the case interviewed for this article. Mr. Cosma declined to comment.

Just a few hours later, however, the operation fell apart, when Mr. Dogaru received a warning that the police were tapping his cellphone. Today, six months on, the fate of the paintings is still unknown, as law enforcement authorities in Romania and the Netherlands, as well as art lovers around the world, struggle to penetrate the fog of claims and counterclaims about what happened to the masterpieces, from the Kunsthal museum in Rotterdam.