Capitol Police officer Brian Sicknick died of natural causes a day after supporters of President Trump rioted at the Capitol on January 6, the chief medical examiner for Washington, D.C., told the Washington Post on Monday.

Francisco J. Diaz, the examiner, said Sicknick died after suffering two strokes the day after the riot, caused by a blood clot that prevented flow to the base of Sicknick’s brain stem. Then-acting U.S. attorney general Jeffrey Rosen said on January 8 that Sicknick died of “the injuries he suffered defending the U.S. Capitol.”

Two rioters are charged with attacking Sicknick with a chemical irritant. The news will likely hamper prosecutors’ efforts to charge the two rioters with homicide.