Where a defendant seeks in a postconviction petition to challenge his sentence as a violation of the proportionate penalties clause of the Illinois constitution, he must demonstrate both cause for not raising the matter at trial and show that he was prejudiced by not raising the issue at trial.The 1st District Appellate Court affirmed the decision of Cook County Associate Judge James Michael Obbish.On the evening of June 30, 2011, Robert Locke sustained a fatal gunshot wound to the head while sitting in the back seat of a …