Who stole the cookie from the cookie jar? O.J. Simpson, apparently.The former gridiron great was recently caught pilfering the sweet treats from the cafeteria of his Nevada prison - something which is strictly forbidden. According to a source, guards noticed the 66-year-old hiding something under his prison clothes as he walked back to his cell after lunch.When they quizzed him, he revealed a stash of more than a dozen oatmeal cookies, which were then seized. 'O.J. just stood there with a goofy grin on his face as the guard kept digging inside his shirt and throwing the cookies on the floor,' the source told The National Enquirer. Doctors had previously warned Simpson, who is looking noticeably tubby, to ease up on the fat and sugar laden foods and start exercising more because he suffers severe diabetes. And the once-chiseled prisoner, who is serving a 33-year sentence for armed robbery, has been trying to diet but gave up after a few weeks. 'The temptation of the cookies in the prison chow line was too much for him, the source said. At first, his fellow prisoners thought he had smuggled in a cell phone or some other banned item. 'So when the guard started pulling cookies out of O.J.'s shirt, the other inmates started laughing so hard they nearly fell over,' the insider added. The guard could have written up Simpson for the attempted cookie smuggle but he reportedly decided to let him off with a warning. The source said that while Simpson was embarrassed, eating his favorite foods is the only enjoyment he has left.