From Gary Murr:

...in order that everyone is clear on this particular photograph's
lineage: It is one from a series of 26, thirty-five mm exposures taken
on May 24, 1964, by Dallas Times Herald staff photographer, Darryl L. 
Heikes. It appears that Heikes was "hired" by Holland McCombs, on behalf
of LIFE magazine to cover this Warren Commission reconstruction for
TIME/LIFE. This particular series of photographs and their negatives,
and others taken on that day, were "upsent" directly to Will Lang,
Editorial Offices of TIME/LIFE, and "addressed to Pollard from Eamon
Kennedy of Dallas Times Herald..." on the evening of May 25, 1964.

McCombs utilized Heikes on other occasions during the tenure of the
Warren Commission and beyond. This particular series of
photographs/negatives were obviously squirreled away by the powers that
be at LIFE, to the point that Heikes had to write "Miss Kosek" in
October of 1964 and ask for their return in order that "the
negatives...must be returned to our files." Perhaps Gary Mack knows more
about this, but I do possess the correspondence involved in this matter,
as well as copies of the photographs and the contact sheet printed from
this same set of negatives. As far as I can ascertain, LIFE never did
anything with any of this photographic material.