If the detective consulted with his Superior Officer - the Lt. - and did what his Lt. told him to do.....then the detective is being used as a scapegoat when all he did was obey the instructions he got from his "commanding officer."
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If there was any wrongdoing, the Lt. was more at fault and should have received the greater punishment. The Lt. should have been fired and the detective demoted and/or suspended. 
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Perhaps the Lt. should have consulted with a judge, gotten a warrant to obtain a blood sample if the judge would issue one (which, given the facts, was questionable), but, if a warrant was issued, then arrested the nurse for violating a court order.