Yang was sentenced to death with a two-year reprieve at Xi'an Intermediate People's Court in August 2007, while the rest of the grave robbers were given prison terms of between seven years and life.

Ironically, the pictures Yang originally took of Wu's sarcophagus on the computer seized by police not only helped his prosecutors, but also proved invaluable to the experts charged with identifying and reassembling the relic.

"After sending the gang to prison, we stepped up efforts to find where the stone relic went," said Han. "We sent information about the case to the Ministry of Public Security and Interpol."

Archaeologists excavated Jingling Mausoleum between September 2008 and May last year.

"We found a tunnel 18.5 meters long and 2.45 meters wide, with seven patios," said Shi Xiaoqun at Shaanxi History Museum. "There were plenty of colorful murals on the walls of the corridor and tomb room, pictures of guards of honor, acrobatics, gardens with trees, birds and flowers.

"It was obviously a royal tomb and we would have found many more relics if they had not been robbed," he said, adding that records found after the excavation proved it belonged to Wu.

In July last year, police in Xi'an received a tip-off that the sarcophagus was in the United States.

Within months Han and his team flew to Hong Kong to start negotiations with "a man name Mike", who was representing the US antiques dealer who bought the relic.

"We told him that the sarcophagus was a rare Chinese relic that was smuggled overseas and that the antiques dealer should return it," said Han. "We warned that we would seek help from Interpol if necessary."

After two more rounds of talks, which this time involved Xi'an's public security officials and experts from Shaanxi History Museum, the buyers agreed to return the sarcophagus to China.

After arriving at Guangzhou port on April 17, Wu Huifei was back in Xi'an by the end of the month.

"This relic provides real information that will help with the study of the mausoleums, customs and arts from the Tang Dynasty," said Feng Gengwu, Party secretary for Shaanxi History Museum.