Police arrested on Saturday a 42-year-old man on suspicion of mailing radioactive materials to 10 government offices last week with a message claiming nuclear materials were being smuggled to North Korea.

Police arrested Tsugio Uchinishi, of Tokyo’s Nakano Ward, and searched eight locations, including his residence, police officials said.

Uchinishi has admitted mailing the substance, monazite powder, and was quoted by police as saying he wanted to draw attention to his claim that a broker, an acquaintance of the director of a foundation supervised by the Education Ministry, is illegally exporting nuclear materials to North Korea.

Uchinishi, who runs a scrap yard, said he wanted to halt the smuggling of nuclear materials to North Korea and added that he acted alone, the officials said.

Uchinishi also said he was angry that the director of the foundation, who is apparently in possession of a large quantity of monazite powder, had refused to sell some to him, they said.

According to police, Uchinishi mailed 10 envelopes containing a small amount of monazite to 10 government offices, including the official residence of Prime Minister Yoshiro Mori, on June 4, in violation of the Postal Law.

Police said they confirmed that Uchinishi had sent the letters after conducting an analysis of the handwriting on the envelopes.

The Postal Law prohibits the mailing of explosives, combustible materials, or materials with radioactivity above 74 becquerels per gram. Violators are subject to a maximum fine of 500,000 yen.

The name of the broker appeared in a message included in the envelopes. The message claimed the broker is smuggling uranium to North Korea to be used in the production of nuclear weapons.

Hiroshi Ikeda, the director of the foundation, has admitted that he has a stockpile of monazite, which contains the nuclear fuel material thorium, in eastern Japan. He told Kyodo News that he imported the substance 20 years ago when he was running a trading company.