Atd Translation: semieducated Peter specialist

[Mike Jing]

P173.13-19   “The voice in these letters,” Ponghill tapping the pile of
loose sheets in front of him, “far from belongin to some crazy passionate
South European or semieducated Peter specialist, it suggests instead an
hombre who knows full well that something has happened to him, but for the
life of him he just can’t figure what—you know that feeling?—sure, who
don’t?—and he’s tryin to work ‘at through, here on paper, how it was done
to him, and better yet who did it.

What is a "Peter specialist"?