Other details were released, but they are too graphic for publication.
Krupa sent the undercover detective several photographs of his face and his body, investigators said.
A time and date for Krupa and the girl to meet was set up at an undisclosed location in Orlando, and when Krupa arrived there on Monday, he was arrested.
A search of Krupa's vehicle found he had purple boxer shorts and a Kit Kat bar with him, investigators said.
"We have to remember that people who seek out children usually do work or find places to go where they have access to children," said Detective Lori Fiorino, with the Orlando Police Department.
Nancy Wait, with the Volusia County School District, said Krupa has served as a substitute teacher and substitute cafeteria worker for the schools since 2015. He has substituted less than 60 times, and his last job was onFeb. 20, Wait said.
“As soon as we were notified of his arrest, he was permanently removed from the substitute list and disqualified for future employment,” Wait said.
A spokesperson for Walt Disney World said Krupa has been placed on leave pending the outcome of the charges.