On Wednesday, a report in KOAA identified the victims as Windy Wenton, 45, and Nicolette Green, 43. "It makes it seem like someone took a very unnecessary risk in creating the problem in the first place".
Both deputies "attempted to extricate the persons being transported", the news release said. Officials said that the transport van was near the Little Pee Dee River, one of the bodies of water that state officials are watching following the heavy rains of Florence.
"They're still under the water", Richardson told The Associated Press early Wednesday.
Rescue teams were able to get to the deputies, authorities said.
Hurricane Florence has now killed at least three dozen people - including at least eight in SC.
Horry County Sheriff Phillip Thompson stated, "Tonight's incident is a tragedy".
The investigation has been handed over to the South Carolina Law Enforcement Division, the news release said. "People need to know exactly how it happened".
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". One patient was from Waccamaw Mental Health and the other was from the Loris Hospital.
Richardson said the van came across rising water and was carried off the road.
The deputies were transporting the women from Conway, near the coast, to Darlington, about 65 miles northwest, on Tuesday night.
The bodies of the two women were recovered on Wednesday, almost 24 hours after the event began, from the submerged van in the Little Pee Dee River.
The Marion County Coroner has confirmed the deaths of both detainees, who have not been identified.
WLTX-TV contacted Green's family, who released the following statement, saying they want answers. At almost 7 p.m. Wednesday, State Law Enforcement Division spokesman Thom Berry confirmed the bodies had been recovered. This incident is being investigated by the State Law Enforcement Division (SLED).
The van was traveling west on Highway 76 into neighboring Marion County when floodwaters overcame the vehicle.
Gov. Roy Cooper told a news conference Tuesday is was hard for residents to leave home, and it's even harder for them to wait to go back. Due to risky conditions and rising waters, additional search and rescue teams are arriving to assist in the recovery of the vehicle.