House Democrats on Wednesday released a transcript of a deposition from Bill Taylor, the U.S. diplomat who Democrats consider one of their top witnesses in the impeachment inquiry against President Donald Trump.

In his Oct. 22 deposition, Taylor testified at length about his work with two other diplomats, EU Ambassador Gordon Sondland, and former Ukraine special envoy Kurt Volker, as part of an overall effort to improve relations between the U.S. and Ukraine.

Democrats announced prior to the release that Taylor is one of three witnesses scheduled to testify next week in the first wave of public hearings in the impeachment inquiry. Taylor will testify next Wednesday, along with George Kent, the deputy assistant secretary for European and Eurasian affairs.

Democrats highlighted several excerpts from Taylor’s testimony that they believe supports their push to impeach Trump.

One of those is an exchange that Taylor had with Rep. Adam Schiff, in which the diplomat said that he developed a “clear understanding” that U.S. military aid to Ukraine was contingent on Ukrainian President Volodymyr Zelensky publicly committing to opening an investigation into potential Ukrainian meddling in the 2016 U.S. election, as well as into Burisma Holdings, a Ukrainian energy firm linked to Hunter Biden.

Democrats have alleged that Trump abused his office by offering Zelensky with a quid pro quo involving the investigations.

Several witnesses, including Taylor, have testified that they suspected that a quid pro quo was on the table. But so far, none have testified they heard directly from Trump that military aid was contingent on the investigations.

Taylor made it clear in the deposition that his suspicions about a possible quid pro quo were based on information in an Aug. 28 news report in Politico, as well as a second-hand summary of a conversation that Sondland had on Sept. 1 with a top adviser to Zelensky.

Sondland said in a revision on Monday to his initial deposition that he told Zelensky’s adviser, Andriy Yermak, that the U.S. would release the military assistance if the investigations were opened. But Sondland also said that he merely “presumed” that the aid was contingent investigations, and that Trump denied to him in a phone conversation on Sept. 8 that there was no quid pro quo.