A double drowning occured recently in Quintana Roo, Mexico. The victims were both experienced cave divers who had been in the system before.
They were making the first dive of the trip & the first dive of the day, the group was either six or eight in size...and all very 'good' divers. They entered on the B line and came to a 'T' where they made a right turn onto the 'T' (this junction used to be about a 3 to 4 foot visual gap). As they continued the dive one team hit thirds and called the dive for their team (2 guys - one 32, one about 50). On their way back it seems that they swept with their light to the right and saw the line going to the right and just took a short cut (what they did was miss the 'T' which may have been slightly obstructed by a rock formation), after a short while they passed an arrow marker pointing in the opposite direction. They continued on and made a visual jump to the 'E' line and followed it to the end. At this point they were actually at the beginning of the 'E' line and only 200 feet from the surface, but of course there was no visible light. Rather than use a gap reel to try and get out, they turned around and promptly drowned.
Everyone, including certified cave divers, must understand that cave diving is a dangerous activity where the slightest error can lead to death. No diver should be complacent or cavilier just because they are trained. Over confidence can be a killer in this environment.