"It's a bet, then," Rhiana said, "Tell me how the killer did it or wash dishes for a month."

Tanner and Jenny, age 13, nodded.

"Right," Rhiana said. "It happened inside a walk-in safe with locked doors, unbroken, concrete walls, ceiling and floor, no windows or other openings. The victim was alone, killed with a big knife driven into her chest and left there. She couldn't have done it herself. She didn't carry the knife inside with her. Four cops surrounded the house. Two cameras with overlapping fields of view stood behind each cop. They'll testify that no one got past them. The tapes...