"Is Murder in a State Without the Death Penalty a Mitigating Factor in a Federal Death Penalty Case?"

A 6th Circuit panel had said yes, in a case where a man was convicted — under federal law, in federal court — of a murder in a  national forest in Michigan.

From the opinion (PDF):

The question is whether the fact of the location of the body so close to a line that forbids the death penalty...

The body was located only 227 feet within the boundary of the national forest.

...  allows counsel to try to convince one or more jurors that imposing the death penalty in these circumstances would treat life or death in a random and arbitrary way based on chance. The phrase “any mitigating factor” plainly includes information about Michigan’s policy against the death penalty and an argument based on the absence of proportionality in punishment when life or death is made to turn on chance and the lives of other equally guilty psychopaths are spared...

 ADDED: En banc, the 6th circuit voted 12-4 to reverse.