Chuckie Nick got killed for the same reason Sammy DeStefano got killed, he was too dangerous to keep around after Ricca Died. Auippa/Cerone ordered it.
It had nothing to do with Milwaukee or the C.I.A. or anything else. Nobody from Milwakee WOULD EVER go into Chicago and kill a made guy.
It would be suicidal.

Chuckie lived in Melrose Park. He was also very well Dressed and was a good looking guy. You would never know he was that rough by talking to him. He actually was kind of soft spoken. He ran his own crew like most all Made guys do in Chicago. He and Alderisio worked together many times on murders.