A former assistant of disgraced scientist Hwang Woo-suk arrived in the country Saturday night for questioning on the scandal surrounding Hwang's stem cell research.

Kim Sun-jong left Incheon International Airport without talking to reporters, who asked him to comment on the suspicions surrounding him and on Hwang's request for a prosecution probe on him.

Returning from the University of Pittsburgh, Kim appeared before the investigative panel on Hwang's work and was grilled overnight on if he switched Hwang's stem cells with those of MizMedi Women's Hospital in Seoul and if patient-specific stem cells existed.

Kim played a central role in nurturing stem cells out of cloned embryos. He has admitted to manipulating photos of two stem cells to make them look like eleven in Hwang's paper published in the journal Science this year.