I am looking for a jailhouse brief submitted by either Richard Loeb or
Nathan Leopold arguing that if the body regenerates its cell every
seven years, they are not the same person as the one who committed the
crime and they should be released. It could be found under identity,
philosophy, ego or other existential philosophy, but it also might be
found in a Chicago legal reporter or anything submitted for the sixth
circuit for Brief submissions to the court I have already tried typing
the words in google in various combinations. I would prefer a copy of
the brief itself, but will be happy with any references to it in other
publications, so long as they confirm or at least imply the existence
of the brief. There is the chance that the brief was not actually
submitted by Loeb or Leopold, and therefore any brief that contains
the argument stated above will be acceptable provided it was written
before 1964. It might have been referenced in a NY times article at
around the 1950s or 60s, but it also might have been referred to in a
philosophcal publication in existence at around that time. However any
subsequent references are equally acceptable.

This publication (from 1960) has no connection with Leopold or Loeb,
but it does present an argument similar to the one you mention:

Not Married.

"A moment, your Honour; it has everything to do with it. Philosophy is
the law of life, and I am a practical philosopher. I do not believe in
a personal soul for I recognize that all mental activity is ultimately
reducible to nerve processes, which in turn are material or bodily."

"If you mean," said his Honour, "that all thought is ultimately
reducible to modifications of the nerves, especially those of the
brain, we agree. That is necessary if one denies, the soul.''

The prisoner smiled. The court sat at attention, and the woman in the
plaintiff's chair ceased sniffling at this exhibition of mental acumen
on the part of "her man."

"I knew we were of one mind, philosophically at least. Now, it is a
known fact, proved beyond shadow of doubt, that our bodies, with their
nerves and brain cells, change completely in the course of seven
years. Old nerves and cells are cast off and new ones are formed from
the food we consume, until there is nothing left of what was once our
old body. Am I correct?"

The judge nodded. The fact was well known to him as it is to all
scientists, Catholic as well as infidel.

"And we agreed in advance," went on the prisoner, "that I have no
soul. Hence all my personality is made up of my body with its nerve
modifications. Now let me state my point. Seven years ago I married
this woman. Time went on; gradually every nerve and fibre of her body
and mine was cast off and replaced by new nerves and new fibres, until
today our bodies are completely changed from the bodies we had when
first we married. We agree, your Honour, that there is no substantial
soul, only a body, and if this is the case, I am not the same person
who married seven years ago; nor is this woman the woman."
 
http://www.pamphlets.org.au/cts/australia/acts0657.html