An extension for the Massachusetts Attorney General office's investigation into the Berkshire Museum art sales concluded Monday. The museum and the Massachusetts Attorney General’s Office will next file a petition with the Massachusetts Supreme Judicial Court to hear the case over the contested sale of art from the museum's permanent collection.

Since an Appeals Court judge would not allow any further delays in the attorney general's investigation, the case now heads to the highest court in the state.

“The AGO believes that the 40 works at issue are subject to restrictions, which the Museum does not believe exist,” said in a joint filing to the Massachusetts Appeals Court.

At stake are 40 works from the museum's collections, including two major Norman Rockwell paintings, which were estimated to bring $50-60 million at auction in an effort to raise funds for the financially-strapped Pittsfield, Mass. museum. A November sale at Sotheby's in New York was halted after civil suits erupted and the state's attorney general, Maura Healey, got involved.

Some 5,000 documents were reviewed and dozens of interviews have been conducted. Opponents to the sale, including Norman Rockwell's family and the Save the Art group, are pressing for the art to remain in the museum.

The museum and the attorney general’s office announced in a joint statement: “We are working together to resolve this matter, recognizing our shared responsibility for the collection of the Berkshire Museum and to the community the museum serves. We are committed to helping this museum secure its future.”