When Carl Kosak returned from work to his home in Greensburg’s Academy Hill neighborhood, he got something to eat and then headed down to the basement. That’s where he assumed his second identity — one long hidden from co-workers, neighbors and friends — as acclaimed mystery writer K.C. Constantine. “My father had a desk at the bottom of the basement stairs, and that’s where he wrote,” said Kosak’s only son, Chris Kosak of Moraga, Calif. “He wrote every single day — some days maybe that was only one sentence — but he put himself in that chair at that desk...