(CNN) House Intelligence Chairman Adam Schiff on Wednesday announced impeachment hearings will begin next week as Democrats prepare to take their case against President Donald Trump to the public.

Schiff, a California Democrat, said that three witnesses will testify next week: US diplomat Bill Taylor and State Department official George Kent will appear on next Wednesday, and former US Ambassador to Ukraine Marie Yovanovitch is testifying next Friday.

The open hearings mark a new phase of the Democrats' impeachment inquiry into Trump and Ukraine and will be the first time that the country hears directly from the officials at the center of allegations that Trump pushed Ukraine to investigate former Vice President Joe Biden and the 2016 election in order to help the President politically. The hearings are the next step for Democrats as they move closer to impeaching a President for the third time in US history.

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Impeachment investigators have heard from more than a dozen witnesses behind closed doors, piecing together evidence of a months-long campaign spearheaded by the President's personal attorney Rudy Giuliani in Ukraine that included an effort to remove Yovanovitch from her post and then to convince Ukraine to announce an investigation into the Bidens and the 2016 election.

Taylor's testimony is among the most significant for the Democratic case that $400 million in security aid to Ukraine and a one-on-one meeting between Trump and Ukrainian President Volodymyr Zelensky were conditioned on Ukraine announcing investigations into the 2016 election and Burisma, the company that hired Hunter Biden. In his 15-page opening statement, Taylor explained how he was told that "everything" Ukraine wanted was conditioned on the investigation. The is no evidence of wrongdoing in Ukraine by either Biden.

Schiff said Wednesday that public hearings will show "the most important facts are largely not contested" related to Trump's use of "illicit" means to secure damaging information on his political rivals.

"Those open hearings will be an opportunity for the American people to evaluate the witnesses for themselves and make their own determinations about the credibility," Schiff said.

As Democrats begin to shift from the fact-finding depositions toward the public phase of the impeachment probe, the committee released four transcripts of the closed-door interviews, which provided additional detail about the freezing of Ukraine aid and the push for investigations, as well as the removal of Yovanovitch from her post earlier this year.

Schiff told reporters Taylor's deposition transcript would be released later Wednesday.

The committee on Monday released its transcript of Yovanovitch's closed-door deposition, in which she described how State Department leaders would not issue a public statement of support for her amid the Giuliani attacks, out of concern that the President might undermine their efforts.

Kent, a career State Department official, also testified about Giuliani's efforts to oust Yovanovitch and said he was told to lie low after raising concerns about Giuliani undermining US policy in Ukraine.

The Democrats' argument that US security aid and Ukraine announcing an investigation were linked was bolstered Tuesday with the release of US Ambassador to the European Union Gordon Sondland's transcript, which included a major reversal of his testimony that he told a Ukrainian aid the money was unlikely to be released unless an investigation was announced.

Democrats say the transcript of the July 25 call between Trump and Zelensky already shows Trump pressured his Ukrainian counterpart to investigate Biden, but the testimony provides even more evidence that Trump directed Giuliani to run a shadow campaign for Ukraine to launch an investigation.

Republicans, who are considering adding Rep. Jim Jordan of Ohio to the House Intelligence Committee to participate in the hearings, will have an opportunity to use the hearings to poke holes in the Democrats' case against the President.

Jordan criticized Democrats for not bringing back for public testimony US special envoy to Ukraine Kurt Volker, whose transcript was released Tuesday. Jordan pointed to Volker saying he didn't believe there was any quid pro quo.

"No announcement about any investigations took place," Jordan said when asked about Taylor's testimony saying he was told Trump wanted aid withheld in exchange for Ukraine announcement of investigations. "There was no announcement of investigations, no statement, no actual investigation started, so none of that is all happening and it's all based on what someone told someone."

Rep. Mark Meadows, a North Carolina Republican, argued that Sondland "said he didn't know why the aid was held up."

"(He) still doesn't know and certainly from that standpoint, there was no quid pro quo," Meadows said.

The House Intelligence, Foreign Affairs and Oversight committees have conducted the depositions behind closed doors with Trump administration officials who have testified under subpoena over the objections of the White House. The public hearings will be conducted just by the House Intelligence Committee. Under rules passed by the House last week, both Democrats and Republicans will have 45-minute blocks to question witnesses in which staff attorneys can participate.

This story has been updated and will continue with additional developments Wednesday.