The Office of Research Integrity, part of the Department of Health and Human Services, has confirmed to an advocacy group that it is investigating the circumstances of five now-retracted papers for possible academic misconduct. Questions surrounding the research, which involved causing brain trauma to 30 newborn piglets, are piling up, but very little in the way of explanation has been offered by the university that hosted the experiments or the journals that published them.

Between 2016 and 2019, several research papers led by then–University of Pennsylvania pharmacy researcher William Armstead on neuromolecular outcomes following traumatic brain injury were published in a handful of journals, including the Journal of Neurotrauma and Pediatric Research. The research involved administering percussive brain injuries to piglets using a piston that both displaces and deforms neural tissue, according to Retraction Watch.

Earlier this year, five of those papers, all coauthored by Armstead, who is now retired, were retracted at his request due to “substantive questions [that] have arisen regarding the findings, presentation and conclusions reported in the paper that could not be answered with available source data,” according to a retraction notice issued in June by the Journal of Neurotrauma.

Armstead never responded to follow-up questions from the journals regarding the nature of those questions or the validity of the data, nor did he respond to requests for comment from Retraction Watch or The Guardian, the outlets report. Pediatric Research managing editor Lauren Overbey responded to Retraction Watch only to direct questions to the university, but it too has so far failed to respond.

The violent nature of the research, the retractions due to unsubstantiated data, and the lack of answers in their aftermath has drawn criticism from the animal rights group Stop Animal Exploitation Now (SAEN), and Retraction Watch opines that retracting the papers due to potentially fabricated data makes it difficult to justify a project that involved subjecting baby animals to brain damage. And now, the project is the subject of a federal investigation. Specifically, the Office of Research Integrity has begun an oversight review that is typically used in cases of academic misconduct, including falsifying or fabricating data, the Guardian reports.

“Five article retractions in four months is a smoking gun for fraud,” Michael Budkie, a cofounder of SAEN, says in a press release about the investigation emailed to The Scientist.