If you're referring to Officer Sicknick, he died of two strokes a day after being attacked with bear spray by Julian Khater and George Tanios and being subjected to the most stressful day of his life. Medically, he may have died of natural causes, but those strokes were the result of the riot, whether because he was sprayed with bear repellent [1] or because of the stress of the day.

[1]: https://www.nytimes.com/interactive/2021/03/24/us/officer-si...