Police arrested Shi on June 1 after his fingerprint - found at an Internet cafe in Fengtai district of Beijing on May 11 - matched ones from the crime scene.

So far, police have recovered six of the stolen pieces, but the other three, which together have an insured value of 150,000 yuan, remain missing.

Shi felt guilty and also confessed to previous wrongdoings, such as stealing a laptop, a purse with more than 500 yuan and a mobile phone. The court decided to give him 13 years in jail after considering his attitude to the case.

However, Huang Changyong, Shi's lawyer, said the 13-year sentence was heavy for the farmer and will advise Shi to appeal to higher courts.

"The legal authority didn't estimate the value of the stolen artifacts, so it cannot decide such a long sentence for my client," Huang said.

But Han Yusheng, a law professor from Renmin University of China, said the sentence for Shi is not heavy and the result is fair.

The artifacts that Shi stole must be worth a lot of money, even if the court did not consider their insured value, Han said.

In addition, the theft happened in the Palace Museum, which houses many priceless artifacts, according to the professor.

"Shi cannot make up such a loss," he said.

Wang Xing, a Beijing lawyer specializing in criminal cases from Hui Cheng Law Firm, said the dispute about the case also pointed out another question of the crime. "That is how to estimate the value of an artifact."

"In this case, the judge roughly estimated the value of stolen pieces according to their source and age, but such a problem should be studied by our legal workers," he added.

The incident sparked public concern over security loopholes in the Forbidden City in the heart of Beijing.

The museum's new curator, Shan Jixiang, said management had long been aware that the existing alarm system was outdated and a four-year upgrade began in November 2009.

By December, about 60 percent of the work had been completed, according to a report by Xinhua News Agency.