Dr. George Burkley was the personal physician of John F. Kennedy, as well as Dwight D. Eisenhower and Lyndon B. Johnson. He witnessed Kennedy's autopsy, and verified the death certificate and the autopsy face sheet, which is stained in his blood (that's his signature on the bottom-left corner).

Wikipedia article - John F. Kennedy autopsy

Dr. Burkley was not called to testify to the Warren Commission or the House Select Committee on Assassinations. The following comments made by him may show why.

1967 oral history interview:

McHUGH: "I see. Do your conclusions differ at all with the Warren report of the circumstances or cause of death?"

BURKLEY: "My conclusion in regard to the cause of death was the bullet wound which involved the skull. The discussion as to whether a previous bullet also enters into it, but as far as the cause of death the immediate cause was unquestionably the bullet which shattered the brain and the calvariurm."

McHUGH: "I see. The brain and the what?"

BURKLEY: "And the skull, calvarium."

MCHUGH: "I see. Do you agree with the Warren Report on the number of bullets that entered the President's body?"

BURKLEY: "I would not care to be quoted on that."

http://jfkassassination.net/russ/testimony/burkley.htm

1977 HSCA interview report:

...The doctors didn't section the brain and if it had been done, it might be able to prove whether or not there were two bullets. Dr. Burkley thinks there was one but concedes of the possibility of there having been two.

https://www.maryferrell.org/showDoc.html?docId=600&relPageId=5&search=%22concedes_of%20the%20possibility%20of%20there%20having%20been%20two%22

Burkley's affidavit to the HSCA:

Had the Warren Commission deemed to call me, I would have stated why I retained the brain and the possibility of two bullets having wounded President John F. Kennedy's brain would have been eliminated.

http://www.kenrahn.com/Marsh/Autopsy/BURKLEY.TXT

Here is an official memo from HSCA staffer Richard Sprauge:

From: Richard Sprague To: File March 18, 1977

William F. Illig, an attorney from Erie, Pa., contacted me in Philadelphia this date, advising me that he represents Dr. George G. Burkley, Vice Admiral, U.S. Navy retired, who had been the personal physician for presidents Kennedy and Johnson.

Mr. Illig stated that he had a luncheon meeting with his client, Dr. Burkley, this date to take up some tax matters. Dr. Burkley advised him that although he, Burkley, had signed the death certificate of President Kennedy in Dallas, he had never been interviewed and that he has information in the Kennedy assassination indicating that others besides Oswald must have participated.

Illig advised me that his client is a very quiet, unassuming person, not wanting any publicity whatsoever, but he, Illig, was calling me with his client’s consent and that his client would talk to me in Washington.

https://www.history-matters.com/archive/jfk/hsca/numbered_files/box_23/180-10086-10295/html/180-10086-10295_0002a.htm

Author Henry Hurt wrote in his book Reasonable Doubt of a short interview with Burkley:

It is significant that Dr. Burkley had been with the President in Dallas, with him in the Parkland Hospital emergency room, with his body as it was flown east, and present during the autopsy. It is also significant that even though he was the only doctor present both at Parkland and at Bethesda, Dr. Burkley's testimony was never taken by the Warren Commission, nor was it taken later by the House Select Committee.

In 1982 Dr. Burkley told the author in a telephone conversation that he believed that President Kennedy's assassination was the result of a conspiracy.

This startling statement, after so long a silence, amplified an obscure exchange Dr. Burkley had in an oral-history interview on file at the Kennedy Library in Boston.

And also wrote in an endnote:

When he originally telephoned the author, Dr. Burkley expressed his willingness to discuss various matters concerning the assassination. He asked for a letter detailing the areas the author wished to discuss. Dr. Burkley acknowledged receipt of the letter with a letter of his own. Two months later, the author proposed a meeting with Dr. Burkley to discuss the points. The doctor responded with an abrupt refusal to discuss any aspect of the case.

http://krusch.com/books/kennedy/Reasonable_Doubt.pdf

In Michael L. Kurtz's book The JFK Assassination Debates: Lone Gunman Versus Conspiracy, it also says this (I do not have a link to the full ebook), this is excerpted from Barry Krusch's 3-volume series on JFK:

... When informed that if this were true, then the assassin who fired that shot must have been located in front of the president, Burkley stated that he always believed in a conspiracy, a remark that he had previously made to another assassin researcher, Henry Hurt. However, he quickly terminated the conversation without providing any details.

https://i.imgur.com/saphV7V.png