Going by the Global Shark Attack File report posted earlier in this thread (underlining added is mine to address specific questions):
"A boat carrying a large group of divers dropped Jonaitis and Lupold off at a reef wall before taking the rest of the divers for a regular, sanctioned sport dive. It wasn’t known if Lupold and Jonaitis ever reached their desire depth. Photos Lupold had taken of his dive computer showed he reached a depth of 296 feet four minutes into the dive. According to local authorities, the divers were supposed to float a plastic balloon-like marker to the surface when they reached their desired depth, but it was never deployed, and was later found in the vest Lupold was wearing when his body was recovered on Sunday. The dive tank was still on his body but his weight belt was missing, which allowed his body to float to the surface, the Cozumel official said."
So we have them diving without a boat on station, or a descent line, or safety divers and making a descent of about 74 ft per minute. That the max known depth was recorded via a photo of the dive computer suggests it's possible they went deeper than 296, although they either didn't reach their planned max depth or didn't attempt to deploy the SMB.
Other details mentioned were that the accident had occurred on a Friday and the body was found on the surface the following Sunday six miles away from where they went missing. If accurate, that is either a very slow drift of 0.1-0.2 knots in an area of "moderate current" or the body didn't float until some time after death.
The International Shark Attack File record (no association with GSAF) would be more comprehensive, but access is limited to cooperating scientists as it contains confidential items such as autopsy reports, interviews, and photographs.