Yoshiki Sasai, a cellular biologist from Japan, committed suicide following a scandal centered on a paper on which he worked.

STAP cells, short for stimulus-triggered acquisition of pluripotency, were the subject of a paper on which the late researcher worked. Problems were found in the study by other researchers, which developed into a larger scandal.

Sasai was employed as the deputy director at the Riken center for Developmental Biology, located in Kobe, Japan. The biologist hanged himself from a rope attached to a rail in a stairwell at the facility.

The researcher left at least five suicide notes, three near his body and two on the desk of his administrative assistant. In at least one of the messages, Sasai wrote to the lead researcher, "Be sure to reproduce STAP cells."

Satoru Kagaya, spokesperson for the center, would not reveal the intended recipients of the notes, citing privacy concerns. The public relations representative said the late researcher had appeared to become physically and emotionally tired over the last few months.

Haruko Obokata headed the controversial research into STAP cells. A pair of articles on the subject was published by the journal Nature, which claimed that regular cells in mice could be transformed into stem cells when exposed to a weak acid.

These papers became the targets of critics who questioned the credibility of the study. The articles were retracted by the journal in July, who cited five groups of errors, including mislabeled images, and deceptive captions.

"These multiple errors impair the credibility of the study as a whole and we are unable to say without doubt whether the STAP-SC phenomenon is real... given the extensive nature of the errors currently found, we consider it appropriate to retract both papers," Nature editors wrote in their retraction of the pair of papers.

Sasai edited and supervised the researched conducted by Obokata, and was greatly affected by the criticism, feeling he was responsible for not recognizing errors in her study.

"I am overcome with grief at this terrible news. The scientific world has lost a talented and dedicated researcher, who earned our deep respect for the advanced research he carried out over many years," Noyori Ryoji, president of Riken wrote in a statement to the press.

The 52-year-old had received counseling in March 2014 for stress and depression over the scandal.

Obokata is conducting further research into STAP cells, attempting to see if the results of the original study can be confirmed. She is conducting her study at the Riken Center.