President Lee Myung-bak's only son was allowed to return home Friday after around 14 hours of questioning by special prosecutors over alleged wrongdoing in a land deal for his father's retirement home project.

"I explained as much as I can," weary-looking Lee Si-hyung told reporters, emerging from the Seoul office of the independent counsel probing into suspicions that the 34-year-old attempted to misuse taxpayers' money through the now-scrapped land deal.

He came out of the building at half past midnight.

Asked about whether he thinks he has been unfairly accused, he said he does "not feel aggrieved."

He sidestepped a question about whether he feels sorry about facing a criminal investigation as the son of a president.

"I sincerely answered (the investigators' questions)," he just said before hurrying to leave the site, packed with reporters and television crews, in a gray van.

He appeared before the counsel as a criminal suspect, dealing another heavy blow to his father's administration in its final months. The president's elder brother, Lee Sang-deuk, was indicted in September on bribery charges.

The president is scheduled to retire in February after a five-year term.

It marked the first time in South Korean history a child of a sitting president has undergone face-to-face interrogation by special prosecutors.

Last year, Lee Si-hyung and the presidential security service jointly bought a plot of land in Naegok-dong on the southern edge of Seoul to build the president's retirement residence and auxiliary facilities for security personnel.

The junior Lee is under suspicion of not sharing the cost evenly, with the security service paying an extra 600 million won ($542,000) to 800 million won. Opposition parties claim it was a scheme to enable the son to profit at taxpayers' expense.

The special prosecution team headed by Lee Kwang-bum, a former judge, questioned Lee Si-hyung over charges of attempting to misappropriate taxpayers' money, officials said.

Accusations against the younger Lee also include using the wrong name in the real estate transaction, the officials said. (Yonhap News)