Even though the verdict absolved the defendant of criminal responsibility he has the right to appeal the finding.
Commonwealth v. Bruneau, Mass. No. SJC-11820, 8/27/15
Unlike an acquittal, the special verdict given in this case finds that he commited the criminal act, but makes him ineligible for civil comittment. The Massachusetts Supreme Judicial Court ruled that the defendant has a right to appeal as a person who is "aggrieved by a judgment." This aggrievment is based on the harsh consequences that flow from a verdict of "not guilty by reason of insanity."
http://www2.bloomberglaw.com/public/desktop/document/Commonwealth_v_Bruneau_No_SJC11820_2015_BL_275264_Mass_Aug_27_201
