When we evaluate cases for potential Muslim terrorists, we always look for physical signs like a trimmed mustache and a beard that is lesser trimmed. And when it comes to a crime that was committed, we look at who the victims are. In the story on Eddie Routh, who murdered Chris Kyle, there are signs of concern, especially the facial hair, it does match the profile of a convert.
Also, Routh was a prison guard over Muslim terrorists at Bilad Airbase in Baghdad in 2007. He never served in battle, but spent most of his time looking and talking to Muslims in jail. He could have likely interacted with the inmates and got converted; prison has a higher conversion rate than any mosque. Also, why would he kill a Navy seal who was known to have killed so many terrorists?