WASHINGTON — Capitol Police Officer Brian Sicknick, 42, who was injured while confronting rioters during the Jan. 6 insurrection, suffered a stroke and died from natural causes, the Washington, D.C., medical examiner’s office ruled Monday, a finding that lessens the chances that anyone will be charged in his death.

Investigators initially believed the officer was hit in the head with a fire extinguisher, based on statements collected early in the investigation, according to two people familiar with the case. And they later thought Sicknick may have ingested a chemical substance — possibly bear spray — that may have contributed to his death.

But the determination of a natural cause of death means the medical examiner found that a medical condition alone caused his death — it was not brought on by an injury. The determination is likely to significantly inhibit the ability of federal prosecutors to bring homicide charges in Sicknick’s death.

U.S. Capitol Police said that the agency accepted the medical examiner’s findings but that the ruling didn’t change the fact that Sicknick had died in the line of duty, “courageously defending Congress and the Capitol.”

“The attack on our officers, including Brian, was an attack on our democracy,” police officials said in a statement.