A state appeals panel last week declined to vacate an 18-year-old’s life sentence for murdering three people, including an 11-year-old girl.The 1st District Appellate Court found defendant Denzel Pittman’s natural life sentence did not violate the proportionate penalties clause of the Illinois Constitution, rejecting comparisons to other cases where 18- and 19-year-olds had life sentences vacated on appeal.Pittman was convicted of stabbing his 17-year-old girlfriend Jade Hannah, her mother Stacy Cochran and her …