"We want those who are responsible to be held accountable", it reads in part.
The Department of Public Safety says all of Interstate 95 in SC is now open.
The van was carrying the detainees to a different facility in Darlington, South Carolina when it was overtaken by flood waters on Tuesday.
It is not immediately clear why such a transfer was attempted given the preponderance of flooding in the area due to Hurricane Florence.
Richardson said the van came across rising water and was carried off the road.
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.
Rescue crews needed about 45 minutes to find the van, which was underwater at that point, and plucked the Horry County deputies from the roof, the sheriff said.
We are working hand-in-hand with the State Law Enforcement Division to cooperate in this investigation.
The Lumber River as of September 19 was still in "major" flood stage in several places, according to the National Weather Service. They were going down Highway 76 when the floodwaters began to rise near the Little Pee Dee River, which is a branch of the Lumber River.
Officials said the van was near the Little Pee Dee River, one of the bodies of water state officials were watching following the heavy rains of Florence.
Carolinas Interstate 95 Shut Down Again Great Pee Dee flooding shuts down thoroughfare
Floodwaters in North Carolina were still quite high as of September 19.
The National Weather Service has confirmed that the remnants of Hurricane Florence spawned a total of six tornadoes in Virginia earlier this week.
North Carolina officials say a body has been found in a trailer near the flooding Cape Fear River.
The incident is now being investigated by the State Law Enforcement Division.
The van was attempting to cross a flooded area of Highway 76 in Marion County when it got swept away, according to cops. Two deputies were rescued but the detainees died.
Sixteen North Carolina rivers were at major flood stage Tuesday, with an additional three forecast to peak by Thursday. The two deaths will push Florence's toll across three states to almost 40 victims.
On Wednesday, the sheriff said the vehicle had not yet been recovered yet due to unsafe conditions and rising waters.
Neither woman was handcuffed or restrained, Richardson said.
The two individuals being transported were confirmed dead by the Marion County Coroner.
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