Timothy Borger, 48, disappeared during a scuba training exercise at Lake Pleasant Regional Park in Peoria, Arizona, on October 16, 2010. He and a diving group descended near the submerged Old Waddell Dam; at about 56 feet below the surface Borger became separated from his companions and did not resurface.

The Maricopa County Sheriff’s Office Dive Team carried out an extensive search and recovery campaign, conducting more than 60 missions using divers, underwater rovers and cadaver dogs. The old dam’s breached, collapsed structure—massive concrete slabs, rebar and other debris at depths beyond 250 feet—creates deep voids and shifting silt that investigators say likely concealed him. An obituary published in 2011 states that Borger drowned; his body has never been recovered and the case remains unresolved.

Does anyone who dove Lake Pleasant or trained there around 2010 recall conditions near the Old Waddell Dam or saw anything that might explain how Borger became separated from his group?