Every time a high profile crime is committed and LE doesn't have someone in custody inside of an hour, all of the armchair criminologists and Hitman-playing "wetwork specialists" on the Farms immediately declare that we have a highly intelligent ghost agent on our hands and the perp will never be found.
"But the guy isn't a serial killer or terrorist who just blew up a building." This was a murder committed seemingly for ideological reasons, that's pretty much the definition of terrorism. Very powerful people have been spooked, I absolutely guarantee you the FBI and counterterrorism units are working on this. The shooter is not going to get away from this alive.