You mean a law like [18 U.S.C. section 242](http://codes.lp.findlaw.com/uscode/18/I/13/242)?\n\nTL;DR: An officer of the courts who knowingly violates a citizen's civil rights is subject to federal prosecution for the act.  If that civil rights violation results in death, the officer can face the death penalty.  This can be prosecuted by the federal government regardless of jurisdiction, as it's enacted under the auspices of the 14th Amendment.