abc s alex perez in kenosha again tonight. reporter: tonight, new details on the teenager investigators say showed up in kenosha armed with a rifle and allegedly opened fire on demonstrators protesting the police shooting of jacob blake. authorities arrested 17-year-old kyle rittenhouse in nearby illinois for his alleged role in tuesday s shooting that left two dead and one injured. police identified him as the man seen in this social media video during protests that night. so, nonlethal, but you guys respond? we don t have nonlethal. so you guys are full-on ready to defend the property? yes, we are. reporter: this graphic video capturing the chaos. a crowd appears to be chasing the armed man when he falls to the ground and starts firing. as police approach the scene, rittenhouse can be seen with his hands up, but he s never taken into custody. when someone i ve been in a shooting before in situations that are high stress, you have such an incredible tunnel vision.