by her husband. When Johnson took the bottle, Williamson knocked it out of his hand, admonishing him to never drink from a bottle that he had not personally seen opened. Johnson replied, "Don't ever knock a bottle out of my hand." Soon after, he was offered another (poisoned) bottle and accepted it. Johnson is reported to have begun feeling ill the evening after and had to be helped back to his room in the early morning hours. Over the next three days his condition steadily worsened. Witnesses reported that he died in a convulsive state of severe pain. The musicologist Robert "Mack" McCormick claimed to have tracked down the man who murdered Johnson and to have obtained a confession from him in a personal interview, but he declined to reveal the man's name. While strychnine has been suggested as the poison that killed Johnson, at least one scholar has disputed the notion. Tom Graves, in his book Crossroads: The Life and Afterlife of Blues Legend Robert Johnson, relies on expert testimony from toxicologists to argue that strychnine has such a distinctive odor and taste that it cannot be disguised, even in strong liquor. Graves also claims that a significant amount of strychnine would have to be consumed in one sitting to be fatal, and that death from the poison would occur within hours, not days. In their 2019 book Up Jumped the Devil, Bruce Conforth and Gayle Dean Wardlow suggest that the poison was naphthalene, from dissolved mothballs. This was "a common way of poisoning people in the rural South", but was rarely fatal. However, Johnson had been diagnosed with an ulcer and with esophageal varices, and the poison was sufficient to cause them to hemorrhage. He died after two days of severe abdominal pain, vomiting, and bleeding from the mouth. The LeFlore County registrar, Cornelia Jordan, years later and after conducting an investigation into Johnson's death for the state director of vital statistics, R. N. Whitfield, wrote a clarifying note on the back of Johnson's death certificate: In 2006, a medical practitioner, David Connell, suggested, on the basis of photographs showing Johnson's "unnaturally long fingers" and "one bad eye", that Johnson may have had Marfan syndrome, which could have both affected his guitar playing and contributed to his death due to aortic dissection. Gravesite The exact location of Johnson's grave is officially unknown; three different markers have been erected