https://judiciary.house.gov/sites/democ ... %20v.3.pdf
It includes this quote.
"One noteworthy result of President Trump’s obstruction is that the House has been improperly denied testimony by certain government officials who could have offered first-hand accounts of relevant events. That does not leave the House at sea:there is still robust evidence, both documentary and testimonial,bearing directly on his conduct and motives.
But especially given the President’s obstruction of Congress, the House is free under the Constitution to consider reliable testimony from officials who overheard—or later learned about—statements by the President to witnesses whose testimony he has blocked.240To summarize: just like grand jurors and prosecutors, the House is not subject to rigid evidentiary rules in deciding whether to approve articles. Members of the House are trusted to fairly weigh evidence in an impeachment inquiry. Where the President illegally seeks to obstruct such an inquiry, the House is free to infer that evidence blocked from its view is harmful to the President’s position.It is also free to rely on other relevant, reliable evidence that illuminates the ultimate factual issues. The President has no right to defy an impeachment inquiry and then demand that the House turn back because it lacks the very evidence he unlawfully concealed.If anything, such conduct confirms that the President sees himself as above the law and may therefore bear on the question of impeachment."