(CNN) -- China has freed the last of four Japanese nationals who allegedly entered a military zone without authorization, Chinese state media reported Saturday.
The four were suspected of illegally entering the area and videotaping military targets, Xinhua news agency said.
But their company said last month that they were sent to China for a Japanese government project to reclaim World War II chemical weapons left by Japan's Imperial Army.
Sadamu Takahashi, the last one freed, was released on bail and instructed to write a statement of repentance, Xinhua said, citing state security authorities in Hebei province
The other three were released on September 30, state media reported.
The group worked for Fujita Corp., a midsize Japanese construction company that Goldman Sachs Group acquired in April 2009.