Daisuke "Dice-K" Enomoto, a former executive of Livedoor Co. who has been training to become the first Japanese space tourist, is suspected of failing to declare some 3 billion yen in income from stock deals, sources said Friday.

Of the 3 billion yen that was allegedly not declared in three years through 2004, the Tokyo Regional Taxation Bureau apparently believes the 35-year-old investor deliberately hid about 500 million yen and has imposed several hundred million yen in back taxes on him, the sources said.

Enomoto has already declared his income for the period and paid the back taxes, they said.