the wall. as gary tuchman shows us. what you re watch are chicago police protecting their own. a human shield of supporters and fellow cops surrounding commander evans as he leaves a courtroom in september of last year. commander. reporter: highly decorated cop charged with aggravated battery and official misconduct after tackling ricky williams in january 2013 on chicago s south side. police say evans was patrolling the area when he saw williams with a gun. evans chased williams down and tackled him in an abandoned home. the defendant then stuck his smith & wesson, .45 caliber, semi automatic pistol deep down the victim s throat. reporter: prosecutors say dna matching ricky williams was found on commander evans pistol. the gun williams was carrying, police say, was never found. and williams filed a complaint saying the officer threatened to kill him. this is how former police boss