Thompson planned to address reporters later Wednesday.
Marion County Coroner Jerry Richardson told the Associated Press early Wednesday that the van was still underwater.
Richardson said the van came across rising water and was carried off the road. The bodies were recovered later that evening.
Neither woman was handcuffed or restrained, Richardson said.
Both deputies "attempted to extricate the persons being transported", the news release said.
"Deputies are supposed take care the people that are in the back of their auto", Rose Hershberger, Green's 19-year-old daughter, told WMBF News.
Under South Carolina law, people who have been certified by a physician as posing an imminent risk of harm to themselves by virtue of mental illness and are the subject of an involuntary emergency admission must be transported by law enforcement to whichever designated hospital has agreed to admit them, according to officials with the state's Department of Mental Health. After about 30 minutes, she was told her mother was being hospitalized and would be transferred to a mental hospital but was never given a reason why. Police said a court order allowed them to transport Green and Newton. Holden wouldn't give further details on the victims' status, citing an ongoing state police investigation.
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"She was like a normal mom and the best mom anyone could ask for", Hershberger told the station. "Just like you, we have questions we want answered". Don't Drown?' Gross negligence has robbed two families of their loved ones.
A statement sent by the Green family, including her other living child, to WLTX, added: "We want those who are responsible to be held accountable". Greenville Online reports that neither woman had a criminal record.
Thompson said he did not think the women were in restraints in the back of the van, noting that restraints are used for combative patients "and I understand they were not". By the time they got there, the van was underwater, and the deputies were on the roof.
Green-Johnson did not immediately respond to a request for comment from HuffPost. CNN's request for the names of the deputies has not been answered.
The coroner in neighboring Marion County confirmed the two deceased patients were female, and the South Carolina State Law Enforcement Division is investigating the incident, according to the statement.
Bishop and Flood have been placed on administrative leave while three separate investigations are conducted into the deaths.