Burden-shifting-in-criminal-trial

QUESTION PRESENTED Before trial, the district court barred the Government from commenting that the defense had the opportunity to conduct independent forensic testing on the firearms which were the subject of prosecution. That order was to prevent impermissible burden shifting. Only if the defense “put on evidence” or “noted that the Government failed to test the firearms for DNA and fingerprints” could the Government comment in closing. The Government did so nonetheless, flouting the pretrial order. Is this sort of burden-shifting, no matter the strength of the Government’s case, so improper and contrary to the presumption of innocence that a new trial is warranted?