The ruling, released Monday, likely will make it difficult for prosecutors to pursue homicide charges in the officer’s death. Two men are accused of assaulting Sicknick by spraying a powerful chemical irritant at him during the siege. In an interview with The Washington Post, Francisco J. Diaz, the medical examiner, said the autopsy found no evidence the 42-year-old officer suffered an allergic reaction to chemical irritants, which Diaz said would have caused Sicknick’s throat to quickly seize. Diaz also said there was no evidence of internal or external injuries... Diaz said Sicknick suffered two strokes at the base of the brain stem caused by a clot in an artery that supplies blood to that area of the body. Diaz said he could not comment on whether Sicknick had a preexisting medical condition, citing privacy laws.