That intruder was apprehended because the “mouse ears” cap he was wearing struck an observant airman as odd. 
An inspector general’s investigation found three main security failings, starting with “human error” by a gate security guard who allowed the man to drive onto the base even though he had no credentials that authorized his access. Hours later, the man walked undetected onto the flight line by slipping through a fence designed to restrict entry. Finally, he walked onto and off a parked airplane without being challenged, even though he was not wearing a required badge authorizing access to the restricted area.