Sasai, who was 52 years old, was considered an expert on embryonic stem cells, but his reputation took a serious hit when the lead author of the Nature papers, Haruko Obokata, was accused of scientific misconduct in April. The two scientists worked very closely together on the stem cell papers that described a new, simple way of transforming adult cells into embryonic-style stem cells. But Sasai spoke out against certain aspects of his own research during a news conference in April, while maintaining that he thought the experiments provided hints of a breakthrough. Still, he told The Wall Street Journal during that time that he felt "overwhelmed with shame." He later penned an apology in which he lamented not being able to identify the errors before the studies were published.

Ryoji Noyori, a nobel prize laureate and the president of Riken, said in a statement that Sasai was "invaluable to the global scientific community," and that he was stunned by the news. Sasai reportedly left suicide notes on his secretary’s desk, as well as at the site of his death — a biomedical research center located near the Riken Center.