They're accused of killing Irina Yarmolenko, 20, a Chapel Hill High School graduate, who 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.
At a news conference Friday, Police said little about the details of the case. They refused to give a motive or more details about Yarmolenko's final hours.
Previously, they said on the day she died, Yarmolenko made several stops in her car. She was seen taking bags out of it at a Goodwill, and later she went to a credit union and a coffee shop.
Police also pulled data from the black box in her car and say it shows someone was sitting in the passenger seat as the car was rolled towards the water.
"This is not closure for us. This is just one step in the investigation," offered Chief David B. Belk.