Well who placed them there: Fritz or Studebaker? Your own story is at
odds. You forgot to mention that Alyea said he saw them in the nest BEFORE
Fritz gave them back to Studebaker to be placed there to be photographed.
This is from Alyea's account:
"The height of the stack of boxes was a minimum of 5 ft. I looked over the
barricade and saw three shell casings laying on the floor in front of the
second window in the two window casement. They were scattered in an area
that could be covered by a bushel basket. They were located about half way
between the inside of the barricade. I set my lens focus at the estimated
distance from the camera to the floor and held the camera over the top of
the barricade and filmed them before anybody went into the enclosure. I
could not position my eye to the camera's view finder to get the shot.
After filming the casings with my wide angle lens, from a height of 5 ft.,
I asked Captain Fritz, who was standing at my side, if I could go behind
the barricade and get a close-up shot of the casings. He told me that it
would be better if I got my shots from outside the barricade. He then
rounded the pile of boxes and entered the enclosure. This was the first
time anybody walked between the barricade and the windows."
"Fritz then walked to the casings, picked them up and held them in his
hand over the top of the boxes for me to get a close-up shot of the
evidence."
Then later this: "Over thirty minutes later, after the rifle was
discovered and the crime lab arrived, Capt. Fritz reached into his pocket
and handed the casings to Det. Studebaker to include in the photographs he
would take of the sniper's nest crime scene."
So Alyea's account is that he saw the casings on the floor, Fritz picked
them up and pocketed them. Then later Fritz gave them to Studebaker to put
back for photographing.
But there's nothing in his account indicating that Fritz put them when
they were first discovered.
Alyea's admittedly confusing account is here:
http://www.jfk-online.com/alyea.html