He was carrying spare clips in his original cargo pants... yes? What else could have been in them? Makes perfect sense to confiscate his clothing.
Hell..., they probably had to also make sure he didn't have a something else stuffed up his arse. You never know with a crazy person willing to mass murder people, who had been planning this for about a month (according to his manifesto)
Actually to be honest if it is the actual shooter from El Paso funny they said he died then who the hell is this guy that the cops are padding down funny if you have a sharp eye for detail in the proper police training you'll notice the difference which I'm not claiming I have gone through but I can tell those two videos do not match or those two pictures