“The judge instructed the jury that closing arguments are not evidence, and that it was their duty to determine the facts and to apply the facts to the law as explained by the judge. The judge also properly instructed on the meaning of reasonable doubt. In light of these instructions, and the strength of the Commonwealth’s case, we are confident that the ill-advised comment would have had no effect on the jury’s verdict,” Justice Frank M. Gaziano wrote on behalf of the unanimous Massachusetts Supreme Judicial Court