BEIJING — A Beijing court on Friday sentenced a former employee of the Forbidden City to be executed for stabbing two of his supervisors to death on the museum's grounds, state media reported.

Zheng Zhibiao argued at his trial in early December that he had been concerned over a lack of protection of artifacts held at the former palace of China's emperors, the state-run Beijing News said.

The vast network of ceremonial halls, imperial apartments and other buildings is Beijing's premier tourist attraction.

Beijing News said Zheng, a display designer at the museum's exhibition division, had complained about a lack of professionalism in protecting the museum and its collections as well as in renovating its buildings.

It wasn't clear what prompted him to kill the two supervisors, although the paper said prosecutors argued he had a personal grudge.

All death sentences must be automatically reviewed by China's supreme court.