But when he opened the door, there was his son, playing a song on the keyboard and mimicking lyrics in a pitch-perfect melody.
"Music is what unlocked John's tongue," Grant Thompson said.
Through song, John Mikkiah Thompson, now 18, has found a way to overcome his limitations and express himself in ways he never knew possible. He also will release his first album of original music this month and headline a concert at Center Grove High School on Sunday.
His goal is to become a contemporary Christian music star.
But he also hopes to be an inspiration to other people struggling with autism, letting them know that the condition doesn't mean they can't achieve their goals.
"It feels good to know I'm moving people. People come up to me afterward crying, and it's very interesting to hear that I touch their lives when I start to sing," he said.
Image: Hands playing a keyboard, via Shutterstock.