The president of Stanford University, Marc Tessier-Lavigne, said that he’s resigning after months of scrutiny over flaws in his research.

A Stanford committee said that he didn’t engage in any “fraud or falsification of scientific data,” but identified manipulation of research data by those in his lab, according to a letter he sent Wednesday.

“I should have been more diligent when seeking corrections, and I regret that I was not,” he wrote. “The panel’s review also identified instances of manipulation of research data by others in my lab. Although I was unaware of these issues, I want to be clear that I take responsibility for the work of my lab members.”

Tessier-Lavigne said he’s stepping down effective at the end of August.

The initial questions over his research were raised by the university’s student newspaper, the Stanford Daily.