Comment by kreetx

Well, the larger sequence of events goes back to the group of people interfering with police work, including the woman whistling along with an officer. She got pushed which was where Alex entered. (Alex had already had a brief contact with the officers minutes before the fatal sequence of events.) Alex also had a gun with him. This eventually led him to being shot.

The researched why will surface likely soon. But as of now, carrying a gun to a protest isn't something that helps with looking harmless.