(NewsNation) — One of the world’s largest consulting firms is under a Department of Justice investigation for its role in advising companies on how to promote opioids.

The criminal investigation into McKinsey & Company was years in the making and the prosecutors are examining advice given to pharmaceutical companies on how to market the highly addictive medications.

Tens of thousands of deaths in the U.S. have been blamed on the opioid epidemic, in part driven by aggressive marketing of addictive pain medications by pharmaceutical companies.

Defense attorney David Katz said a judgment against McKinsey could lead to compensation for those affected.

“Hopefully, if the Justice Department makes a huge civil recovery from McKinsey, it will be shared with victims,” he told NewsNation.

The focus of the investigation is determining whether McKinsey was part of a criminal conspiracy in its work advising pharmaceutical companies on marketing strategies to boost sales. The firm is also under investigation for conspiracy to commit healthcare fraud when companies selling opioids allegedly made fraudulent claims to programs including Medicare.

Prosecutors are also looking into obstruction of justice after McKinsey disclosed it had fired two people for discussing deleting documents related to opioid work.

Katz said he suspects there is more to that investigation.

“I think the two people involved probably made some kind of plea agreement that might be sealed in some kind of indictment,” he said.

McKinsey previously paid millions in settlements related to lawsuits brought by states, territories, health insurers and other local governments. The company, which stopped advising companies on opioids in 2019, did not admit liability in settlements.

Purdue Pharma pled guilty to kickback conspiracies and fraud in relation to efforts to promote opioids and subsequently declared bankruptcy.