The missing JFK brain is certainly suspicious,but the evidentiary value is up for debate.Dr. Humes examined the brain,noted that the left lobe was virtually intact,took at least seven photos of the brain,and included all of the above in his notes.Before placing the brain in a jar of Formalin,all of the estimated 30 persons present had the opportunity to witness the entire procedure. Out of this number ONE MAN says none of this occurred. The photographs have never been disputed,are not missing,and the report is still able to be accessed.The conclusion of a shot from the rear that killed JFK would not be changed if the brain were found today.Read the actual reports by the attending personnel,and their subsequent statements on the topic,and see if you can find anyone present who believes that anyone in the autopsy room saw any evidence of a third wound to Kennedy.

Secondly,the Grassy Knoll myth lacks substantiation in two very critical respects. One,any witness who says that they saw a puff of smoke from a rifle on the knoll is pretty much delusional,mistaken,or outright full of sh*t. When Stone recreated the puff of smoke scene in his comedy "JFK",he had to use a concealed bellows to get the effect,since they could not find a rifle that emitted smoke.
Second,with the stiff north wind blowing on that day,even if a puff of smoke did exist,it surely would not linger long enough to be noticed,rather it would blow away from the barrel immediately.
On the topic of the supposed 51 witnesses to a grassy knoll shooter,here is a long but worthwhile link that explains a lot.http://mcadams.posc.mu.edu/shots.htm