Why are muslims stabbing policemen in airports, such as the one in Flint, Michigan?

https://www.jihadwatch.org/2017/06/flint-michigan-muslim-screaming-allahu-akbar-stabs-police-officer-in-possible-act-of-terrorism

http://www.washingtontimes.com/news/2017/jun/21/michigan-airport-evacuated-officer-seen-bleeding-n/?utm_source=onesignal&utm_campaign=pushnotify&utm_medium=push

Aren't they such peaceful people?