Trump pressed Zelensky on a July 25 phone call to open those investigations - a conversation whose interpretation lies at the heart of the impeachment inquiry.
Morrison was briefed about the meeting but did not attend.
Questions over that trade-off - military aid and a coveted White House visit for Ukraine's president in exchange for the investigations - are central to the impeachment inquiry. Reports said David Holmes testified behind closed doors that he heard Sondland telling the president Ukraine would move forward to investigate the Bidens - since Zelensky would do "anything you ask him to do".
An adviser to Vice President Mike Pence, who listened to President Donald Trump's call with Ukrainian President Volodymyr Zelenskiy, found the president's reference to investigations into a potential 2020 political opponent and the 2016 election "unusual and inappropriate". She testified to investigators earlier this month, and a transcript of her testimony was released Saturday.
Trump has denied such a quid pro quo, and allies have noted that the military aid was eventually released - and that Zelensky did not know that the aid was being withheld at the time of the call. "The member of my staff could hear President Trump on the phone asking Ambassador Sondland about the investigations - Ambassador Sondland told President Trump the Ukrainians were ready to move forward".
"In the presence of my staff at a restaurant, Ambassador Sondland called President Trump and told him of his meetings in Kiev", he stated.
Holmes said Sondland told Trump that Zelensky "loves your ass" to which Trump responded: "So, he's gonna do the investigation?"
Morrison told impeachment investigators that until he spoke with Sondland on September 1, he hadn't drawn a connection between the hold on military aid - announced inside the administration in July - and the demand to investigate the Bidens.
Morrison reported at least two of his conversations to National Security Council lawyers.
Jennifer Williams, a special adviser to Vice President Mike Pence for Europe and Russian Federation who is a career Foreign Service officer, arrives for a closed-door interview in the impeachment inquiry on President Donald Trump.
The transcripts are of testimony by Jennifer Williams, a special adviser for Europe and Russian Federation to Vice President Mike Pence, and Tim Morrison, the former senior director of European affairs at the National Security Council.
Democrats said the testimonies from Williams and Morrison indicated that Trump's comments "immediately set off alarm bells throughout the White House", House Intelligence Committee Chairman Adam Schiff, House Foreign Affairs Committee Chairman Eliot Engel and acting House Oversight Chair Carolyn Maloney said in a statement.
Lawmakers convened Saturday to interview Mark Sandy. He's the first official from the Office of Management and Budget to defy President Donald Trump's instructions not to testify. Like others, he received a subpoena to appear. Trump says he did nothing wrong.
More public hearings in the House are scheduled for this coming week.