Prosecutors are facing significant hurdles in filing homicide charges in the case of Capitol Police officer Brian Sicknick, who died after the Jan. 6 riot in Washington, D.C., particularly since a suspect has yet to be arrested almost a month after the siege, multiple sources told Fox News. 

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Sicknick, 42, was struck in the head by a fire extinguisher while "physically engaging" with rioters at the Capitol, authorities said. He collapsed once he returned to his division and died at the hospital the next day. 

No cause of death has been given and it is unclear if the blow to Sicknick's head, exposure to chemical irritants during the melee, or something else ultimately contributed to his death. 

Sicknick’s remains were cremated before he laid in honor in the Capitol Rotunda last week, as dozens of law enforcement officials, congressional leaders, President Biden and first lady Jill Biden paid their respects. 

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Fox News was told immediately after Sicknick’s death that authorities would treat the probe as a homicide investigation. 

The FBI and U.S. Capitol Police continue to comb through tips related to Sicknick’s death and are soliciting more every day. The slain officer was one of five people who died as a result of the rioting.

Law enforcement officials have watched hours of surveillance and camera footage captured from that day from multiple angles and have arrested over 200 suspects as a result. 

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Authorities are asking anyone with information to call 1-800-CALL-FBI (1-800-225-5324).