New video helping investigators in search for suspects in US Capitol police officer's death

New video evidence from the US Capitol on January 6 has aided the work of the FBI and prosecutors in the US Attorney's Office in Washington, DC, in what the official says investigators continue to view as a complicated and difficult case.

One leading theory that investigators are considering is that the suspects sprayed an irritant, perhaps bear spray, that caused Sicknick to suffer a fatal reaction, the official said and CNN has previously reported. In police audio played at the impeachment trial Wednesday, officers are heard screaming during the attack that some members of the violent Capitol mob were spraying them with bear spray.

The 13-year veteran of the police force died on January 7, one day after he collapsed in his office after being "injured while physically engaging with protestors," the Capitol Police said in a statement last month.

Investigators have struggled for weeks to build a federal murder case in Sicknick's death as they pored over video and photographs to try to determine the moment when he suffered his fatal injuries. Investigators have determined that initial reports suggesting Sicknick was struck with a fire extinguisher aren't true, CNN previously reported.

Last week, Sicknick lied in honor in the Capitol building in an emotional ceremony, and was visited by President Joe Biden and first lady Jill Biden and congressional leaders.

More than 100 other police officers were injured in the melee last month, including at least 15 officers who required hospitalization, according to court documents.

Several people have been charged with assaulting police officers in the weeks since, but none so far in relation to Sicknick.

Prosecutors have dedicated a team inside the DC US Attorney's Office to investigate the officer's death and other officer assaults.

Sicknick's death is being investigated by the DC Metropolitan Police Department's homicide branch, the US Capitol Police and federal authorities.

Metropolitan Police Department Public Information Officer Sean Hickman told CNN on Wednesday that the case remains under active investigation, and there is no further information available to provide at this time.

Eva Malecki, a spokeswoman for US Capitol Police, said the Sicknick family, respectfully, declined to comment.

This is a breaking story and will be updated.