WASHINGTON (NewsNation Now) — U.S. officials have arrested and charged two men with assaulting U.S. Capitol Police Officer Brian Sicknick with bear spray during the Jan. 6 riot, but they do not know yet whether it caused the officer’s death.

George Tanios, 39, of Morgantown, West Virginia, and Julian Khater, 32, of Pennsylvania, were arrested Sunday. They were expected to appear in federal court Monday.

The idea that Sicknick died after being sprayed by a chemical irritant has emerged in recent weeks as a new theory in the case.

Investigators initially believed that Sicknick 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. But as they’ve collected more evidence, the theory of the case has evolved and investigators now believe Sicknick may have ingested a chemical substance — possibly bear spray — that may have contributed to his death, officials have said.

Khater is the man in a video obtained by the FBI that showed him spraying Sicknick and others with bear spray, according to court papers. The act hasn’t been directly tied to Sicknick’s death.

“Give me that bear (expletive), Khater said to Tanios on the video, according to court papers. Sicknick and other officers were standing guard near metal bike racks, the papers say.

Khater then says, “they just (expletive) sprayed me,” as he’s seen holding a white can with a black top that prosecutors said ”appears to be a can of chemical spray.”

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 supporters on the National Mall to “fight like hell” to overturn his defeat.

The circumstances surrounding Sicknick’s death remain unclear, and a final cause of death has not been determined. Capitol Police have said he died after he was injured “while physically engaging with protesters” and the agency’s acting chief said officials consider it a line-of-duty death.

Sicknick collapsed later on and died at a hospital on Jan. 7. The Justice Department opened a federal murder investigation into his death, but prosecutors are still evaluating what specific charges could be brought in the case, the people said.

The medical examiner’s report on Sicknick’s death is incomplete. Capitol police say they were awaiting toxicology results.

In a statement released by the U.S. Capitol Police after the announcement of charges against Tanios and Khater in Sicknick’s death, Acting Chief Yogananda Pittman thanked the USCP, FBI and MPD for working to identify and arrest those involved in the attack.

“The attack on the U.S. Capitol and on our police officers, including Brian Sicknick, was an attack on our democracy,” said Pittman. “Those who perpetrated these heinous crimes must be held accountable, and — let me be clear — these unlawful actions are not and will not be tolerated by this Department.  I want to thank our skillful USCP investigators as well as our FBI and MPD partners for their work to identify and arrest those responsible for these violent acts, as well as Acting U.S. Attorney Channing Phillips and his staff for their prosecution of these cases.”

The FBI has already released about 250 photos of people being sought for assaulting federal law enforcement officers during the riot. Some have already been arrested, and the Justice Department said about 300 people have been charged with federal offenses related to the riot.

You can read the full affidavit below: