I'm pretty sure they were briefed before they left CA. They were told the reason, the length/width of the lake, the depth, how much water is left, percentage of visibility, etc... However, I'd imagine that they'll need time to get acquainted with all the LE/FBI players working the case, a better idea (visually) of what the conditions are (visibility, plant life, etc). Based on these calculations they'll determine the best place to systematically start. Its a pretty extensive prep/process...I have the pleasure of knowing a few experienced divers...