I respectfully maintain my right to disagree!
Do you recall the beefy officer giving CR the stink eye, and escorting him into the courtroom? For ICE to step in and try to take CR from Iowa, for any reason (other than CR being taken to a Federal facility for execution), that would mandate that they step over that officer's dead body and many like him. IT AIN'T GONNA HAPPEN. Iowa will not give up CR willingly, and ICE is too professional to go in and take him by force (I hope).
However, there are a number of Federal crimes that CR has committed since he lives sub Rosa, as it were. He's committed identity fraud (which comes under the perview of many of the Patriot and Homeland Security laws passed since 9/11), payroll fraud involving Federal witholding with every check he received from his employer, mail fraud if anything involving the above or any Federal assistance he may have received went through the mail, and probably other crimes.
One linkage that I see for a Federal murder charge, is if CR did any of the above to gain employment, and that job gave him access to the vehicle he used in commission of the murder, that allows the Feds to charge him with Homicide and a possible death penalty. There are other ways the Feds can reach this same charge. The Feds aren't going to deport CR, they'll charge him and convict him if they find a need to do so.