His uncle, Steve Hunter, said Mr. Arnold was an avid pilot and was building a light airplane at his home.
Remembering the Navy Yard fallen: 12 diverse stories come to a sudden end →
"He was a loving son of his mother and his wife and great father to his kids," Mr. Hunter said. "It's tragic. How can you get up in the morning and go to work and have that happen? How do bad things like that happen to good people?"