John Kapoor, founder of Insys Therapeutics (INSY) , and four co-defendants were convicted Thursday of running a nationwide bribery scheme to get doctors to prescribe the company's highly addictive opioid painkillers.

A federal jury in Boston convicted ex-CEO Kapoor and his co-defendants after 15 days of deliberation, Reuters reported.

Kapoor, 75, is the highest-ranking pharmaceutical executive convicted in a case tied to the opioid drug crisis. Tens of thousands of overdose deaths linked to opioids are reported annually in the U.S. 

Prosecutors charged that Kapoor oversaw a  scheme to bribe doctors by retaining them to act as speakers at sham events at restaurants ostensibly meant to educate clinicians about the company's fentanyl spray, Subsys. While Subsys was approved in 2012 only for use in treating severe pain in cancer patients,  prosecutors claimed doctors who took bribes often prescribed Subsys to patients without cancer, helping boost sales for Insys.

Kapoor also directed efforts to defraud insurers into paying for the drug, prosecutors said. His co-defendants include former Insys executives and managers Michael Gurry, Richard Simon, Sunrise Lee and Joseph Rowan.

Prosecutors, who called 39 witnesses during the 10-week trial, depicted Insys Therapeutics as a struggling company under intense pressure from Kapoor to succeed.  Several former Insys executives pleaded guilty and testified for the prosecution in the hopes of getting a more lenient sentence.

Shares of Insys Therapeutics were down 1.7% to $4.15