He had a stroke
According to a CNN article on February 2, there is no evidence that Officer Sicknick was hit in the head with a fire extinguisher. He died the following day due to an underlying medical condition, at least according to his brother. He underwent an autopsy conducted by the DC medical examiner with no conclusive findings as to cause of death and no sign of blunt force trauma. Authorities are now considering the possibility that he became ill after being exposed to pepper or bear spray, but they haven’t been able to prove it.