The prosecution Thursday sent a letter to Lee Sang-eun, eldest brother of former Seoul Mayor Lee Myung-bak, summoning him for the probe of alleged hidden wealth of the former mayor.
It was the first time that the prosecution took a legal step to question the eldest brother, who is now in Japan.
The summons is part of the investigation into the former mayor's alleged speculative land transactions. He is a leading presidential hopeful of the main opposition Grand National Party (GNP) and his family is allegedly involved in the land trading.
In 1985, former POSCO Chairman Kim Man-je and Lee's brother jointly bought land from Hyundai Construction and Engineering, of which Lee was president at the time, for 1.5 billion won. In 1995 they sold the land to POSCO Engineering and Construction for 26.3 billion won.