The brain and other material from the autopsy - photos, tissue slides, et cetera - were reportedly placed in a locker and given to the National Archives under the custody/control of JFK's secretary Eveylyn Lincoln. Mrs. Lincoln later said she gave the material to RFK. RFK reportedly had the brain placed in JFK's grave.
Here: https://www.maryferrell.org/showDoc.html?docId=145280#relPageId=165&search=Evelyn_Lincoln
No person but Mrs. Kennedy had legal authority to make a final determination as to her husband's remains.
Any secretive subversion of her sole legal authority in making a final determination as to her husband's remains would have been a criminal act by the secretive conspirators .
The criminal charges just keep piling up in this conspiracy to disappear his brain, absent of the coroners legal written directive that "further examination" take place .
Be that as it may, any item accepted under the roof of the National Archives , makes the National Archives fully responsible for the security of items within it's confines.
To include a fully and specifically documented chain of custody ( Dates, Times, Purposes) of coming and going,
That is unless you are alleging that Mrs. Lincoln also established a domicile for herself within the Archives to personally watch over the container 24/7 ?
So it all boils to down to the United States National Archives chain of custody Document mandated by federal law for each and every item under the roof of the Archives ?
A really simple matter to take all the mystery out of it ?
Have you seen that documentation for the president's brain coming and going at the National Archives ?
Why not do you think ?