No. If the guards gave the gunman, who was aiding and abetting a major felony, armed robbery, a command to drop his weapon, and he refused to, he could be viewed as a deadly threat and shot, at least in the legs/arms.
They could not shoot the unarmed thief except perhaps with a teaser.
If you look at the video and note there was about ten seconds between the smash and both guys running out of the store, no longer a threat, and in Chicago and you tell me you would advise them to shoot them in the back I’d say enjoy your time with Ty in a cell. Second if you do shoot someone the place to aim is center mass not the legs or arms. Third standard answer to the question to why did you shoot is to stop the person from harming you or someone else. In this case they could not make that fly especially with a video. It infuriates me that in 49 states that is the situation. Now in texas what they did would be viewed as “open season”. There you are authorized to protect both life and property. All in my opinion of course.