Neal Cassada's lawyer said his client died at home Sunday morning.
The 55-year-old was scheduled for trial Monday on charges of first-degree murder and criminal conspiracy in the 2008 death of 20-year-old Irina Yarmolenko in Gaston County.
Investigators say the woman was found asphyxiated by the Catawba River May 5. Her Saturn was found at the edge of the water with her body lying next to it. Investigators say it appears someone tried to drive the car into the water.
Defense attorney David Phillips says Cassada had a history of breathing and heart problems and collapsed shortly after 10 a.m. Sunday.
District Attorney Locke Bell says officers are trying to determine if there is evidence of suicide or foul play. Phillips says he's confident the death was from natural causes, noting his client was under stress.
Cassada's cousin, Mark Carver of Gastonia, is awaiting trial.