Japan’s government-affiliated Riken research institute says it found several irregularities in articles on stem cells co-authored by one of its star researchers.

Their lead author is Haruko Obokata. She’s affiliated with the Riken Center for Developmental Biology. Her articles describe a new way of reprogramming stem cells. They were published in January in the journal Nature.

Riken President Ryoji Noyori apologized at a press conference on Friday, saying the institute is considering retracting the controversial articles.

Officials investigating the case presented some of their findings.

They showed how Obokata altered an image demonstrating the reprogramming of a stem cell by pasting in data from another image.

12 lines in her description of the research process are nearly identical to an article published by another researcher in 2005.

Investigators also confirmed allegations that some images were copied from Obokata’s doctoral dissertation, although her thesis submitted in 2011 focused on a different experiment.

Riken officials say they will continue their investigation to determine if these irregularities constitute a case of malpractice.