ROME The Italian government has successfully brokered deals with American museums and private collectors for the return of what it says are looted antiquities. But it is finding the Ny Carlsberg Glyptotek, an art museum in Copenhagen, harder to crack. Talks with the Glyptotek have dragged on for months, even though "the presuppositions for the negotiations are identical to those that were carried out with the Americans," said Maurizio Fiorilli, a lawyer for the Italian state involved in the negotiations. The Glyptotek, however, has "adopted a very different attitude," he said. At the core of the dispute are Etruscan and Greco-Roman objects that the Glyptotek bought from Robert Hecht, an American antiquities dealer now on trial in Rome, where he is accused of receiving and selling stolen artifacts and conspiracy in the antiquities trade. He denies any wrongdoing. The Italians have used evidence from Mr. Hecht's trial, and from the trial of the antiquities dealer Giacomo Medici, who was convicted of receiving and smuggling archeological artifacts, to persuade several American institutions including the Metropolitan Museum of Art in New York and the J. Paul Getty Museum in Los Angeles to return objects to Italy on the suspicion that they were illicitly excavated. (Mr. Medici is appealing his conviction.) Italy's campaign is founded on a 1970 Unesco convention that prohibited the illicit circulation of a nation's cultural property. There is general agreement in the antiquities world that objects that surfaced after that date without established provenance should not be purchased. In addition a 1909 Italian law states that anything found underground in Italy belongs to the state. At Mr. Hecht's most recent hearing last month, correspondence from the early 1970s between him and former Glyptotek officials regarding the sale of dozens of objects to the museum including an Etruscan calesse, or two-wheeled horse-drawn carriage, excavated near Fara in Sabina, just north of Rome was presented as evidence against him. The calesse, which dates from the early seventh century B.C., was part of the funerary accouterments of a Sabine prince whose tomb at a Colle del Forno necropolis was discovered by Italian archaeologists in 1970. When they began excavating soon after, they found that tomb robbers had already been there. "Fortunately the tomb raiders didn't do a thorough job," said Daniela Rizzo, an archaeologist and witness for the prosecution. In later digs the most recent in the fall of 2008 Italian archaeologists managed to recover material from the prince's tomb and other parts of the necropolis. Today the tomb's contents, including amphorae, weapons, gold and silver jewelry and decorations, as well as elements of the calesse, are mostly split between the Glyptotek and the archeological museum in Fara in Sabina. Despite the overwhelming evidence that the tomb objects were looted, Ms. Rizzo said on the stand, the Glyptotek "has always refused to collaborate" and return the artifacts. Ms. Rizzo said the museum should not have bought the objects in the first place. "They were visibly the result of a traumatic action," she said. "It would have been impossible not to know that it had been illegally excavated. Archaeologists can read between the lines." The Glyptotek has declined to speak about the case. In an e-mail message Jette Christiansen, of the museum's department of ancient art, wrote, "As negotiations are currently still going on, we prefer to refrain from discussing the case in public until we have found a solution, satisfactory to all parties involved." Mr. Hecht said in an interview that he first saw the artifacts he sold to the Glyptotek in Switzerland. "It's only supposition that everything came from Etruria but" and here he broke into song "dimmi quando, quando, quando" ("tell me when, when, when"). Paolo Giorgio Ferri, the prosecutor at Mr. Hecht's trial, said he hoped to build a separate case against former officials at the Ny Carlsberg Glyptotek, though the statute of limitations has expired. Mr. Ferri also said he could ask that some of the objects be confiscated as material evidence should Mr. Hecht be convicted. "For now we have to evaluate the good or bad faith of the buyer," said Mr. Ferri, who is still evaluating whether he will press charges against the Glyptotek. "The sin has almost been ascertained, let's see if we will absolve them." Italian authorities have also presented the Glyptotek with a longer list of objects, mostly bought from Mr. Hecht and Mr. Medici, whose provenance it is investigating. They include an acroterion, or pediment decoration, of a winged sphinx; an Etruscan terra cotta antefix, or roof ornament, similar to one returned by the Getty last year; and terra cotta reliefs of warriors on horseback. Italian officials have repeatedly said they did not intend to "empty the museum of its possessions," only to point out the suspect provenance of many dozens of artifacts. Mario Torsello, the president of the Culture Ministry committee charged with recovering allegedly looted artifacts said in a telephone interview that negotiations with the museum were continuing, and that an Italian delegation would travel to Copenhagen to resume talks. "We're confident that we will arrive at an accord that is mutually satisfying," he said. But even if the Glyptotek should return the funerary artifacts from the tomb at Colle del Forno, the calesse would still not be complete. "There are other elements missing," said Paolo Santoro, the archaeologist who has led the excavations at Colle del Forno since the 1970s. "Who knows who bought them?"