Hundreds of Chinese surgeons and medical personnel have been accused of killing death row prisoners by removing their hearts for transplant even before the inmates had been officially declared dead, in a new academic paper.

A forensic review of 2,838 reports in Chinese scientific journals revealed 71 cases where surgeons might have removed a patients’ heart or lungs before a “legitimate determination of brain death.”

“We found that the physicians became the executioners on behalf of the state, and that the method of execution was heart removal,” one of the authors of the study said in a statement.