It may take investigators some time to determine what motivated 24-year-old Muhammad Youssef Abdulazeez to carry out a murderous attack on two military buildings Thursday in Chattanooga, Tenn.
But acquiring that knowledge is crucial to the safety of Americans.
Four Marines died when a gunman attacked first a military recruiting center and then a Navy-Marine training center a few miles away. They appear to have been targeted simply because they represented the United States and its military. As such, they put their own lives on the line to defend the diverse population that makes up America.
That would include Abdulazeez, a Kuwait-born U.S. citizen, who also died in the attack.
Abdulazeez grew up near Chattanooga in a conservative Muslim family. He was liked by high school classmates and earned an engineering degree from the University of Tennessee at Chattanooga.
Authorities were investigating online postings that may suggest Abdulazeez had become influenced by a radical form of Islam. If that is the case, we must learn how and why.
The shooter had traveled several times to Jordan, where an uncle lived. Did something there change the young man who seemed to his friends like a typical American? Was he influenced by calls from Islamic terrorist groups to target American military sites?
The United States does not, and must not, close its doors on the basis of religion or nationality. But there is ample messaging aimed at radicalizing disenfranchised young Muslims here and elsewhere. The two brothers who bombed the finish line of the Boston Marathon in 2013 had fallen under that influence.
If that is what happened in Chattanooga, we need to learn from it.