Most of the other Chicago Justice characters disappeared after the spinoff was axed (with the exception of John Seda, who went back to where he came from), and Peter was the only one lucky enough to be shipped to New York for SVU.
The Peter Stone character actually started out over in the Chicago branch of the franchise as star of the short-lived Chicago Justice.
Hey, at least that was longer than Chicago Justice lasted!
Sadly, he was only destined for two seasons on the show.