Former Riken researcher Haruko Obokata has returned about ¥600,000 that went toward publishing her papers — since retracted — on STAP stem cells in the journal Nature, the research institute said Tuesday.

The money was returned to Riken on Monday after she indicated her readiness through her lawyer earlier this month. The research institute had asked Obokata to return the money in late March.

Riken did not ask her to pay back money she used in her research because experiments were actually conducted and it was therefore difficult to say she misused her research funds, according to the government-backed institute.

Riken spent nearly ¥40 million to verify experiments conducted by her team and look into allegations that data used in the papers had been falsified. It shouldered the expenses, based on internal rules.

In January 2014, Obokata and her fellow scientists published two papers in the British science journal, claiming they succeeded in creating STAP cells, or stimulus-triggered acquisition of pluripotency cells, which they said can grow into any mouse body tissue.

Heralded as a potentially groundbreaking study, the findings caught global attention, but questions quickly mounted over their veracity, prompting an investigation that later concluded Obokata fabricated data used in the papers.

The papers were subsequently retracted. Failing to replicate the findings, Riken has come to deny the existence of STAP cells. One of her co-authors committed suicide and Obokata left the institute late last year.

On Tuesday, a team of lawyers representing Obokata issued a statement saying that although they have not accepted the conclusion of Riken's investigation, they have decided to avoid further disputes.

On what Obokata's is doing now, one of the lawyers said, "Although I have been able to keep in touch with her, her physical condition continues to be bad."