CBS just put out its May-sweeps release and included in it was a pretty big clue about who bites it on CSI: Miami's May 22 season finale:

"As Horatio mourns the murder of someone close to him, he and the team go on a manhunt to find the killer. Meanwhile, the lab's future is put in jeopardy when the mole is finally revealed (season finale)."

At least I think it's a pretty big clue.