A toxicology report from Prince‘s autopsy obtained by The Associated Press reveals that the icon had an “exceedingly high” concentration of fentanyl in his body when he died. On April 21, 2016, Prince, 57, was found alone and unresponsive in an elevator at his Paisley Park estate in Minnesota. He was later pronounced dead after CPR attempts were unable to revive the singer.

According to Dr. Lewis Nelson, chairman of emergency medicine at Rutgers New Jersey medical school, “the amount in his blood is exceedingly high, even for somebody who is a chronic pain patient on fentanyl patches.” Dr. Nelson called the fentanyl concentrations “a pretty clear smoking gun.”

The toxicology report states that the concentration of fentanyl in Prince’s blood was 67.8 micrograms per liter. It further explains that fentanyl fatalities have been documented in people with blood levels ranging from three to 58 micrograms per liter. Experts state there is no “lethal level” at which fentanyl can kill, but believe a potentially lethal amount of fentanyl was found in Prince’s stomach. A person who takes prescription opioids for long periods of time is able to build up a tolerance, and a dose that could kill one person, might help another.