(CNN) -- The House Intelligence Committee's impeachment inquiry wraps up its series of public hearings on Thursday morning with two key witnesses -- President Donald Trump's former top Russia adviser Fiona Hill and counselor for political affairs at the US Embassy in Ukraine David Holmes.
Both witnesses testified behind closed doors in recent weeks, but Thursday's hearings will be the first time Americans will get to hear from them directly and at the same time.
What are the hearings' schedule and format?
The hearing on Thursday are expected to follow the same format of the previous public hearings.
The committee's chairman, Democratic Rep. Adam Schiff of California, and the top Republican on the panel, Rep. Devin Nunes of California, will kick off the hearings with opening statements.
The witnesses will then be sworn in and get to deliver their own opening statements.
Schiff and Nunes each then get 45 minutes to question the witnesses and are expected to cede part of their time to Daniel Goldman, the panel's director of investigations, and Steve Castor, the House Oversight Committee GOP counsel.
After that, additional rounds of questioning are possible. Each lawmaker on the committee will then get five minutes to ask the witnesses questions.
Who is Fiona Hill?
A former national security official, Hill served in the Trump administration from April 2017 until July of this year.
In her previous closed-door deposition, Hill told Congress about what she called "wrongdoing" in American foreign policy, and testified that former national security adviser John Bolton had encouraged her to report her concerns to the National Security Council's attorney. Hill also said US Ambassador to the European Union Gordon Sondland told Ukrainian officials in meetings on July 10 they would have to open an investigation to secure a meeting between Trump and Ukrainian President Volodymyr Zelensky.
Who is David Holmes?
Holmes is perhaps best known as the US diplomat who overheard Trump ask Sondland about the status of "investigations" during a cellphone conversation in a Kiev restaurant over the summer.
He told lawmakers in his closed-door deposition on November 15 that he'd "never seen anything" like the call Sondland placed to Trump at the restaurant.
"This was an extremely distinctive experience in my Foreign Service career," Holmes said, according to a transcript of his deposition that was released Monday night. "I've never seen anything like this, someone calling the President from a mobile phone at a restaurant, and then having a conversation of this level of candor, colorful language. There's just so much about the call that was so remarkable that I remember it vividly."
Holmes is a career foreign service officer who arrived in Ukraine in 2017. He joined the foreign service in 2002, according to the American Foreign Service Association, and has previously served in Kabul, New Delhi, Kosovo, Bogota, Moscow and Kosovo. Holmes has also served as a special assistant for South and Central Asia to former Under Secretary of State for Political Affairs Bill Burns and spent time on the National Security Council staff at the White House as director for Afghanistan from 2011 to 2012.