The University of Tokyo said Friday that four researchers it previously employed were involved in covering up phony data in a number of thesis papers found to contain falsifications.

Releasing the findings of an in-house probe, the university said it could not verify whether Shigeaki Kato, a former professor in its bioscience lab, and three others tampered with data in the papers supervised by Kato.

But it concluded that they took part in concealing the falsification of image data in five of the 51 papers in question released between 1996 and 2011.

Kato, a leading expert on molecular biology found to have masterminded the cover-up, denied his alleged role, telling Kyodo News, “I am responsible for creating an environment which gave way to problems, but I neither ordered nor tolerated such misconduct.”

Of the others, former assistant professor Jun Yanagisawa and former special lecturer Hirochika Kitagawa were involved in the five thesis papers in which the university found falsifications in experiment images.

Former associate professor Kenichi Takeyama cooperated in fabricating and tampering with the researchers’ experiment notebooks, the report said.

The university also pointed out that the misconduct occurred because of Kato’s high-handed attitude toward researchers.

The four researchers have left the university.

According to an interim report released in December, the university found inappropriate data such as the use of unrelated images in 210 sections of 51 theses that were released from 1996 to 2011, but has yet to identify those involved.