At least 71 death row inmates in China had their vital organs removed, to be used for transplants, before they were officially declared dead, according to a study published in the American Journal of Transplantation.

"We found that the physicians became the executioners on behalf of the state, and that the method of execution was heart removal," an author of the study, Matthew P. Robertson, said in a statement to Al Jazeera.

For decades, per the study, Chinese surgeons have broken a crucial transplant donor rule: Don't remove organs from a live body.

The authors of the study, Australian National University researcher Matthew P. Robertson and cardiac surgeon Jacob Lavee, reviewed 2,838 cases to determine that 348 "surgeons, nurses, anesthesiologists, and other medical workers or researchers" who participated in the executions of inmates between 1980 and 2015 had removed the organs of death row inmates prior to "legitimate determination of brain death."

The World Medical Association, which maintains ethical guidelines for physicians in more than 100 countries, specifies that organ removal should not be the cause of death for transplant donors.

"The dead donor rule is fundamental to transplant ethics," the study reads. "The rule states that organ procurement must not commence until the donor is both dead and formally pronounced so, and by the same token, that procurement of organs must not cause the death of the donor."

The cases showed that medics did not accurately check that inmates were brain dead — unable to be brought back by ventilation or other means. The study authors were able to determine this by manually reviewing 310 papers that mentioned the word "donor."

"If the reports we examine are accurate, they indicate that heart and lung procurement by the surgeon was the proximate cause of the prisoner's death, thus directly implicating the surgeon in the execution," the study reads.

"This was one of the strongest pieces of evidence of failure to adhere to the dead donor rule because ventilation via intubation is a key step in being able to diagnose brain death," Lavee said in a statement to Newsweek.

"There were several other problematic features of these clinical case reports. For instance, the donors did not have intravenous lines established until moments before surgery, and several papers referred to acute brain death. This evidence suggests that the donors' organs were procured before they could have been properly diagnosed as brain dead," Lavee added.

During this time period, there was no process for voluntary organ donation in China, and death row inmates accounted for all transplants.

Dr. Frank Montgomery, Chair of Council of the WMA, told Insider via email that it "has always denounced organ harvesting from executed prisoners as unethical," adding that their interventions helped China outlaw the organ harvesting of inmates in 2015.

"We are now awaiting a clear commitment of our Chinese member organization that this unethical practice is no longer performed in China," Montgomery added.

Yaqiu Wang, senior China researcher at Humans Right Watch, is also seemingly skeptical about whether the country has ceased the practice.

"The Chinese authorities have a history of dubious claims with regard to organ transplantation: They said they had taken organs from executed prisoners but insisted the prisoners had always had consented, despite evidence to the contrary," Wang said in an email to Insider.

"Authorities also claimed that they have ended the practice of using organs of executed prisoners, but there is a lack of evidence on that. The Chinese government's organ donation registry also lacks transparency and there have been reported data discrepancies," Wang added.

China is regarded as the world's leading executioner, according to Amnesty International.

China's death row is shrouded in secrecy. It keeps its figures on executions secret, but Amnesty International estimates that it killed thousands of prisoners from 2016 to 2020. The US government, conversely, killed 13 prisoners during that time period following a 17-year hiatus that former President Trump ended.

"The findings are disturbing, and the Chinese government should respond to these new allegations," Wang said.

The Embassy of the People's Republic of China in the United States of America, Amnesty International, and Lavee did not immediately respond to Insider's request for comment.