WASHINGTON (AP) — Capitol Police Officer Brian Sicknick, 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 the 42-year-old 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. “The United States Capitol Police will never forget Officer Sicknick’s bravery, nor the bravery of any officer on January 6, who risked their lives to defend our democracy."

Federal prosecutors have charged two men with using bear spray on Sicknick during the Jan. 6 riot. The arrests of George Tanios, 39, of Morgantown, West Virginia, and Julian Khater, 32, of Pennsylvania, were the closest federal prosecutors have come to identifying and charging anyone associated with the five deaths that happened during and after the riot.

Lawyers for the two men had no immediate comment Monday.

Sicknick died after defending the Capitol against the mob that stormed the building as Congress was voting to certify Joe Biden’s electoral win over Donald Trump. It came after Trump urged his supporters to “fight like hell” to overturn his defeat.

Sicknick was standing guard with other officers behind metal bicycle racks as the mob descended on the Capitol.

“Give me that bear shit,” Khater said before he reached into Tanios’ backpack, according to court papers. Tanios told Khater “not yet” because it was “still early,” but Khater responded that “they just f---ing sprayed me.” Khater was then seen holding a can of chemical spray, prosecutors say.

As the rioters began pulling on one of the racks, Khater was seen with his arm in the air and the canister in his hand while standing just 5 to 8 feet from the officers, authorities said.

In February, Sicknick became only the fifth person in history to lie in honor in the Capitol Rotunda, a designation for those who are not elected officials, judges or military leaders. He was interred at Arlington National Cemetery.

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Balsamo reported from New York. Associated Press writer Alanna Durkin Richer contributed to this report from Boston.