Former National Security Adviser John Bolton knows about “meetings and conversations” relevant to the House impeachment inquiry that have “not yet been discussed in the testimonies thus far,” Bolton’s lawyer told Congress in a letter on Friday. According to The New York Times, attorney Charles Cooper said his client was “personally involved” in such meetings, but did not offer more details about them. Bolton did not show up to a deposition scheduled for Thursday because, according to Cooper, he wants a judge to rule whether or not he and his ex-deputy Charles Kupperman should defy White House guidance and testify. House investigators have withdrawn a subpoena for Kupperman’s testimony, and indicated they would not seek one against Bolton to avoid court proceedings. However, lawmakers reportedly have suggested using Bolton and Kupperman’s refusal to testify as evidence of obstruction of Congress by the president—which is an article of impeachment.