This story first published October 22 ahead of Laura Cooper's closed-door deposition. It has been updated with additional developments since her initial testimony.

Washington(CNN) A top Pentagon career official overseeing Ukraine policy, who testified to House impeachment investigators that former US special envoy to Ukraine told her Ukrainian officials were alarmed that US security aid was being held up, is set to testify publicly Wednesday as the probe rounds out the second week of its public chapter.

Laura Cooper, the Deputy Assistant Secretary of Defense for Russia, Ukraine, and Eurasia, told the House Intelligence Committee behind closed doors last month that Kurt Volker, the former US special envoy for Ukraine, told her that Ukrainian officials were alarmed in August that US security aid was being held up -- an indication Kiev was aware of the delay earlier than it was reported publicly.

Cooper, who said she met with Volker in August, testified that Volker told her in their meeting that he was attempting to lift the hold on the aid by having the Ukrainians deliver a public statement that they would launch the investigations being sought by President Donald Trump.

Her public hearing this week will be among the nine that House Democrats are holding with current and former administration officials who are tied to the matters they are probing. Although her testimony last month did not contain major revelations or accusations that hit at the core of the Democrats' impeachment case, her interview provided lawmakers with technical details about how the aid was held up -- and how the Ukraine hold diverged from the norm -- and her televised hearing this week will allow her to repeat those details to the American public in real-time.

As a top official overseeing US policy toward Ukraine, Cooper, who visited the country earlier this month as part of an official delegation traveling there, would have been involved with overseeing US military assistance to Kiev, assistance such as the $250 million aid package that was frozen by the Trump administration despite the Pentagon's recommendation that it go forward.

What motivated the White House to order that freeze has formed a central part of the impeachment inquiry into Trump.

Earlier in October, the Pentagon's chief legal officer requested that Defense Department agencies identify, preserve and collect any and all documents relating to the provision of security assistance to Kiev.

Ahead of Cooper's deposition last month, the top US diplomat in Ukraine Bill Taylor testified that he had been told Trump would withhold military aid to the country until it publicly declared investigations would be launched that could help his reelection chances -- including into former Vice President Joe Biden, according to a copy of Taylor's opening statement obtained by CNN.

Cooper first joined the Department of Defense in 2001. She held a series of posts at the Pentagon before taking on her current assignment.

She has been a vocal advocate for US support for Ukraine in the face of what she called the "threat from Russia," telling an audience during a 2018 visit there that "going forward, the US intends to continue providing security assistance support to Ukraine across all domains, including maritime, by providing equipment to support its most critical operational needs."

Her visit came shortly after Russian military forces seized Ukrainian vessels and sailors in the Kerch Strait.

"I want to be clear that the United States will remain committed to building the capacity of Ukraine's military, to include its naval forces," she added, citing progress Ukraine's government had made in reforms as the reason the US would continue supporting its military.