On August 10, an airport worker commandeered an empty commercial plane at Sea-Tac International Airport and flew for more than an hour before crashing on Ketron Island.

Horizon employee Richard Russell, age 28, died in the fiery crash. His last words were captured on cockpit recordings with air traffic controllers. But the incident stirred up inquiries about airport security, flight training, and Russell's motives.

Danny Punturo is Russell's older stepbrother. He spoke to NBC about their family dynamics and the many questions surrounding the man they called "Beebo."

As for what prompted Russell to steal the plane, Punturo thinks past concussions from playing high school football could have played a role in Russell's mental health.

"I hate to speculate, but that's really the only thing that fits."

Punturo addressed the comment Russell made about learning to fly by playing video games. Punturo believes the comment was made as a joke:

Punturo also believes the incident could have potentially been avoided by tighter airport security. "For me, it's more frustrating how he did it, than why he did it. In my mind, it should've never happened."

Full coverage of stolen plane crash