Story highlights Potential evidence in the case has been sent to a lab for analysis

Jesse Matthew is wanted on suspicion of abduction with the intent to defile

University of Virginia student Hannah Graham was last seen September 13

An investigation into her disappearance is ongoing

Authorities have obtained an arrest warrant for Jesse Matthew, charging him with abduction with the intent to defile, in the case of missing University of Virginia student Hannah Graham, Charlottesville Police Chief Timothy Longo told reporters Tuesday.

Police believe Matthew was the last person with Graham before her disappearance. She was last seen September 13 in an area of Charlottesville known as the downtown mall.

The Charlottesville Police Department is circulating a wanted poster for the 32-year-old Matthew, who is also wanted for two counts of reckless driving.

He is described as an African-American man, standing 6 feet, 2 inches tall, and weighing 270 pounds. He is known to have contacts in Maryland, New York, Pennsylvania, Virginia and Washington, D.C.

Matthew willingly went to a police station over the weekend, along with several family members, walking through the front door and asking for a lawyer, Longo said. There was no warrant for his arrest then.

Hannah Graham was last seen September 13.

Matthew and the lawyer spoke and then left, Longo said. The police chief declined to provide additional details on the case.

"Between now and the time that this matter goes to trial, we need to be very sensitive about the information that we share," he said.

However, the chief stressed: "We absolutely are continuing our search for Hannah."

On the evening of September 12, she was seen at a party before friends saw her at an apartment complex a couple of blocks away. That was shortly before midnight, according to a time line compiled by CNN affiliate WVIR

About 12:45 a.m. on September 13, a surveillance camera caught her outside a pub, about three-quarters of a mile from the apartment complex. A doorman turned her away at the pub, Longo said Sunday.

Ten minutes later, she is seen running past a gas station -- no one appears to be pursuing her -- and witnesses say they saw her five minutes later roughly four blocks from the gas station, WVIR reported. She was at a restaurant, witnesses said.

The surveillance camera at an Italian cafe captured her walking along the mall about 1:06 a.m. The camera at a jewelry store recorded her passing two minutes later, WVIR reported.

At 1:20 a.m. she texted her friends to say was lost and trying to find a party, WVIR reported. She and a man were seen having drinks at a bar between 1:30 and 2 a.m., WVIR said.

Police believe she may have been under the influence of alcohol, and may have been vulnerable or unable to defend herself.

Investigators have previously searched Matthew's apartment and car. Potential evidence was sent to a lab for analysis.

Jeffrey Ban, central laboratory director at the Department of Forensic Science in Richmond, Virginia, declined to say how long that work might take.

"Some cases are much quicker than others, just depends on the evidence -- depends on how much evidence we have, where the evidence is, how small the sample is," he said.

"The best I could tell you is that my staff, in a case like this, is very dedicated and they're doing everything they can in the quickest manner possible," Ban said.

Authorities are offering a $50,000 reward for information leading to the safe return of Graham, 18, a second-year student at the University of Virginia.

"Hannah is beyond precious to us," her parents said in a statement released shortly after her disappearance. "We are truly devastated by her disappearance. It's totally out of character for us not to have heard from her, and we fear foul play."