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In this April 16, 2014 photo, Yoshiki Sasai, deputy chief of the RIKEN Center for Developmental Biology, speaks during a press conference in Tokyo. Police said Sasai, 52, was found Tuesday, Aug. 5, 2014, at a government science institute RIKEN in Kobe, western Japan. Sasai had supervised and co-authored stem-cell research papers that had to be retracted due to falsified contents. (AP Photo/Kyodo News) JAPAN OUT

TOKYO (AP) — A senior Japanese scientist embroiled in a stem-cell research scandal has apparently committed suicide, police said Tuesday.

Yoshiki Sasai had supervised and co-authored stem-cell research papers that had to be retracted due to falsified contents.

Hyogo prefectural police said Sasai, 52, was found Tuesday at a government-affiliated science institute RIKEN in Kobe, western Japan. Sasai was deputy chief of RIKEN's Center for Developmental Biology.

A security guard found him suffering from cardiac arrest, with a rope around his neck, according to RIKEN. Sasai was rushed to a hospital but was pronounced dead two hours later.

Police said Sasai left what appeared to be suicide notes, but refused to disclose their contents.

Public broadcaster NHK said he had three letters, each addressed to Haruko Obokata, a co-author of the research papers, as well as senior members of the research center and his fellow researchers.

Sasai's team retracted the research papers from British science journal Nature over co-author Haruko Obokata's alleged malpractice, which she has contested. Retractions of papers in major scientific journals are extremely rare, and the scandal was a major embarrassment to Japanese scientific research.

In two papers published earlier this year in the journal Nature, the researchers reported that they successfully transformed ordinary mouse cells into versatile stem cells by exposing them to a mildly acidic environment. Scientists hope to harness stem cells to grow replacement tissue for treating a variety of diseases.


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RIKEN later held Obokata, a main author of the research, responsible for falsifying data. The investigation also focused on Sasai and two other employees, though the three were not accused of research misconduct.

Sasai had said he was "deeply ashamed" over the problems in the papers.