Following an investigation, Las Vegas police concluded there were no signs of foul play and declared Liston's death a heroin overdose. "It was common knowledge that Sonny was a heroin addict," said Sgt. Caputo, one of the investigating police officers, "The whole department knew about it." The date of death listed on his death certificate is December 30, 1970, which police estimated by judging the number of milk bottles and newspapers around the front door of the property. Coroner Mark Herman said traces of heroin byproducts were found in Liston's system, but not in amounts large enough to have caused his death. Also, scar tissue, possibly from needle marks, was found in the bend of Liston's left elbow. The toxicology report said his body was too decomposed for the tests to be conclusive. Officially, Liston died of lung congestion and heart failure. He had been suffering from hardening of the heart muscle and lung disease before his death. Liston had been hospitalized in early December, complaining of chest pains.