"Thirty years ago, one of the most valuable paintings of the 20th century vanished. It wasn't an accident and it wasn't some elaborate movie heist. It was a simple theft — and it's still a mystery."

"It was the day after Thanksgiving in 1985. Staff at the University of Arizona Museum of Art in Tucson were getting to work, just like any other day."

"'It was almost 9 o'clock so the museum was gearing up to open the doors,' says museum curator Olivia Miller. 'The security guards opened the doors for one of the staff members, and two people followed behind.'"

"It was close enough to opening time that the guards let the man and woman come in. They started climbing a flight of stairs to the second floor, and the guard followed. In the middle of the stairwell, the woman stopped and turned to chat with the guard. Her partner continued on up."