Prosecutors said Monday they were closely analyzing documents seized from the headquarters of Hyosung Group over suspicion that the country's 26th-largest conglomerate evaded a massive amount of taxes.

The Seoul Central District Prosecutors' Office last week raided the company's headquarters in central Seoul to obtain computer hard drives and documents, including accounting books, after the country's tax agency had filed a charge against the group's chairman, Cho Suck-rai, 79, for allegedly leading the tax evasion scheme through various illegal methods.

The family-owned conglomerate had allegedly evaded corporate taxes worth 1 trillion won ($900 million) for the past 10 years since 1997 through an accounting fraud, according to the tax office that had conducted a special audit into the group for months beginning in May.

Cho is additionally accused of holding shares under borrowed names since the 1990s to evade transfer and income taxes worth more than 100 billion won, the prosecutors said.

State prosecutors said they are trying to focus on finding out the details surrounding the alleged tax evasion and the exact amount.

Meanwhile, Hyosung Group officials, who were in charge of the group's finance, will be summoned by prosecutors for questioning later in the day, prosecutors said.

The prosecution office said it will also soon call in a Hyosung Group executive, only identified as his surname Koh, for questioning sometime soon. Koh is suspected of playing a key role in managing the assets of Chairman Cho and his family.

The tax office has already banned Cho and two others -- Koh and Vice Chairman Lee Sang-woon -- from leaving the country pending investigation results.

The group, with more than 11 trillion won in assets, has businesses mainly in the fields of energy and heavy industry.

One of the chairman's nephews is a son-in-law of former President Lee Myung-bak.

According to industry sources, two of the chairman's sons are competing to secure stakes in the group's flagship company Hyosung Corp., a textile and heavy machinery maker, in a bid to gain control of the group's management. (Yonhap News)