From the PBS summary.
Trump "stated on more than 30 occasions that he does not 'recall' or 'remember' or have an 'independent recollection' of information called for by the questions," the Mueller report noted. Other answers were deemed "incomplete" or "imprecise." And when Mueller's team requested a follow-up with Trump to ask more questions, he declined.
Following the submission of Trump's questions, there were questions of whether Mueller would issue a subpoena to have the president testify before a grand jury — but that never happened. The Mueller report explains why on pg. 418: It could have meant a protracted legal battle that would have delayed the investigation.
The report also said: "We determined that the substantial quantity of information we had obtained from other sources allowed us to draw relevant factual conclusions on intent and credibility, which are often inferred from circumstantial evidence and assessed without direct testimony from the subject of the investigation."
From pg. 418 of the report:
April 18, 2019
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April 19, 2019
Voices4America Post Script. Mueller concluded that Trump's written answers - 30 occasions of "I don't know," " I don't recall" - were "inadequate," but felt a prolonged legal fight was not appropriate. Ask yourself. Is this how an honest President behaves? #Unfit4Potus #impeachTrump.
Read the actual answers here. From CNN.
https://www.cnn.com/2019/04/18/politics/trump-written-responses-to-special-counsel/index.html