I agree, but suggest that chain of custody was broken before the investigation started. I believe the body was recovered by fellow divers as opposed to police divers, and the computer could have been swapped out before the body even came to the surface. Obviously I doubt that this happened, but I think that the fact that it could have happened compromises the evidence.
I would suggest that if you decide to abandon your buddy, and leave them lying on the bottom, rather than attempting to rescue him or her, and do whatever first aid you can because you want to preserve the chain of custody for the evidence, you are going to be enjoying a lot of police interest.
You also probably owe it to any prospective buddies to let them know that you won't be bringing them up with you if they get in trouble, to avoid contaminating the evidence.