At one point during the saga, Mr. Seipel embarked on a wild-goose chase in Italy engineered by someone claiming to be the thief. The hoaxer said he was fatally ill and wanted to return the Cellini work before he died.

The art robbery took place in the early hours of May 11, 2003, when Mr. Mang climbed a scaffolding that had been built around the museum while its facade was being sandblasted and broke in through a second-floor window. Police officials said he had first seen the sculpture while on a guided tour of the museum, but their accounts of how he decided to steal it differ. In one account, he noticed the scaffolding around the museum and, having had a bit too much to drink, decided to climb up and steal the Cellini. But others, including Mr. Seipel, say that the job was well planned and could not have been pulled off on the spur of the moment.

When Mr. Mang entered the gallery where the Cellini sculpture was kept, he set off a movement-detection alarm. For reasons that have never been explained, the security guard on duty simply turned off the alarm and failed to investigate, Mr. Seipel said. If the guard had followed normal procedure, the museum director said, he would have turned on lights inside the building to allow video cameras to record whatever was taking place.

"If he had switched on the lights, maybe we would have never lost the 'Saliera,' because the thief would have found himself caught in the flare and maybe he would have just run away." Mr. Mang smashed the glass case holding the Cellini and escaped with it, apparently through the window and down the scaffold.

Ernst Geiger, the Austrian police inspector in charge of the case, has been quoted in news reports as saying that because of his expertise in alarm systems, Mr. Mang knew he had enough time to get away before he would be caught. But Mr. Seipel said the crucial ingredient in Mr. Mang's success was "a sleepy security guard who didn't do his duty."

For about two years, Mr. Mang, who was divorced and lived alone, kept the sculpture under his bed in his Vienna apartment, continuing his life as a security-alarm salesman. Then, in October, Mr. Geiger said, he contacted the company that had insured the sculpture and demanded 10 million euros for the return of the work. He provided Neptune's trident to prove that he indeed had the sculpture in his possession.