Fiona Hill, the former National Security Council senior director for Europe and Russia, and David Holmes, the political affairs counselor at the U.S. embassy in Kiev, Ukraine, will testify Thursday in the impeachment probe into President Donald Trump.

The PBS NewsHour is hosting live coverage of the hearings beginning at 9 a.m. ET. Watch in the video player above.

Hill told lawmakers in closed-door testimony last month that then-National Security Adviser John Bolton expressed concerns that the Trump administration was trying to pressure Ukrainian officials.

Holmes testified behind closed doors that while he was at a restaurant, he overheard Gordon Sondland, the U.S. ambassador to the European Union, speaking to Trump over the phone about “investigations.” The call came on July 26, a day after Trump asked Ukraine’s president to investigate 2020 presidential candidate Joe Biden and his son, Hunter.

That July 25 call has become the focus of the impeachment inquiry. Lawmakers are seeking answers on whether Trump tied that investigation to U.S. aid for Ukraine.

The House Intelligence Committee has heard from several witnesses this week and last week in the public phase of the impeachment probe.

READ AND WATCH: Guide to the impeachment hearings