(CNN) — More than a week has passed since University of Virginia student Hannah Graham disappeared, and police are certain that somebody must know something.
“Somebody’s got to know where she is, and we want to know who that person or persons are,” Charlottesville Police Chief Timothy Longo told reporters Sunday.
Specifically, authorities want to talk to Jesse Matthew, a man Longo believes was the last person with Graham.
Graham, 18, was last seen September 13 in an area of Charlottesville known as the downtown mall.
Using surveillance video and witness statements, authorities have tracked Graham along the mall, where she was seen walking with a man Longo thinks was Matthew.
“I believe Jesse Matthew was the last person she was seen with before she vanished off the face of the Earth,” the police chief said. “We want to talk to him.”
Authorities have searched Matthew’s apartment and car but have declined to say what — if anything — was found. They are offering a $50,000 reward for “information leading to the cause” of Graham’s disappearance.
Matthew willingly went to a police station this weekend, walking through the front door and asking for a lawyer, the police chief said.
Matthew and the lawyer spoke and then left, Longo said, giving detectives no clearer picture of what may have happened the day Graham disappeared.
Separately, police have obtained an arrest warrant for Matthew on suspicion of reckless driving. While authorities were tracking his movement, they saw him get into a car and drive so fast and so dangerously that police were forced to back off, Longo said.
The police chief added: “I hope and pray that we might have an opportunity to talk to Jesse Matthew again because I think he can help up find Hannah Graham.”
CNN’s Chelsea J. Carter and Eric Fiegel contributed to this report.