Thieves made off with a company safe containing some 250 grams of potassium cyanide over the weekend in Onga, Fukuoka Prefecture, police said Monday.
Employees at precision machinery manufacturer Sanwa Shokai reported at around 8 a.m. that the safe, which contained no cash, was stolen from the second-floor room of the firm's president.
The amount of cyanide is enough to kill more than 1,600 people, police said. About 0.15 grams of cyanide can kill an adult within minutes.
Police said several people were apparently involved in the burglary, thinking the safe contained money. Because the firm is located in a mountainous area, it is possible the robbers discarded the safe once they realized there was no money in it.
Investigators have enlisted the help of firefighters and riot police to comb the area for the safe, they added.
The firm, which designs and manufactures industrial machinery, had used the cyanide to increase the hardness of machinery parts. The cyanide in the safe was purchased in October 1980, but company officials said the firm has not used the lethal substance for than 10 years.
Police said the theft probably took place sometime between 5 p.m. Saturday, when it was last confirmed that everything was in order at the firm, and Monday morning. The thieves apparently entered by breaking a glass door on the second floor after climbing an outer stairway.