Prosecutors investigating the Hwang Woo-suk research scandal say that a former assistant to the stem cell scientist was responsible for fabrications that ultimately debunked major papers co-authored by Hwang and his team.

The prosecution said Tuesday that it had secured testimony from the assistant, Kim Sun-jong, that he had single-handedly swapped the stem cells mentioned in a thesis published in Science magazine in 2005 with stem cells from fertilized eggs from MizMedi Women’s Hospital.

Investigators also believe that Hwang had no clue about the fabricated stem cells until last October, when a TV documentary show raised suspicions over the veracity of his research.

Prosecutors are still investigating whether Hwang embezzled money from the flood of grants and other funds that were raised for his stem cell research, adding that the scientist will face major punishment if he is found guilty of misappropriating the money.

Last December, Hwang asked prosecutors to investigate whether his now fraudulent patient-specific stem cells had been switched with ordinary stem cells from fertilized eggs, claiming that Kim had made the switch and had fabricated research results.