Great explainer from a 22-year prosecutor, current defense attorney.

At the time of Mr. Floyd’s death — according to the Medical Examiner — his body was experiencing the effects a drug overdose consisting of a lethal level of Fentanyl toxicity.

George Floyd could not breathe because George Floyd’s lungs were full of fluid. That was not caused by Derek Chauvin’s knee across George Floyd’s neck.

[...]

Any prosecutor with significant experience recognizes the problem here. The Medical Examiner will not be able to say the actions of the officers caused the cardiopulmonary arrest which resulted in George Floyd’s death — not given the level of Fentanyl toxicity in this blood. George Floyd’s respiratory system, under the influence of Fentanyl as it was, suffered from pulmonary edema which resulted in cardiopulmonary arrest during the application by the officers of standard techniques of restraint and control. Based on the Report, the Medical Examiner will not be able to testify that, beyond a reasonable doubt, those techniques caused the pulmonary edema that resulted in the cardiopulmonary arrest that killed George Floyd. Nothing about the techniques leads to pulmonary edema. Without that medical testimony, this case never makes it to the jury.