University of Virginia student Hannah Graham’s death has been ruled a homicide but the method was “undetermined,” Albemarle County police said late Tuesday.

The chief medical examiner’s office in Richmond determined the cause of Graham’s death to be “homicidal violence” but did not specify what killed her. It is the first time that Graham’s death has officially been called a homicide.

Albemarle police and prosecutors said they are continuing to investigate. They said in a statement that they would not answer questions or release additional information “to protect the integrity of the case” and that they are “working hard to ensure that justice is served.”

Graham, 18, a U-Va. sophomore from Fairfax County, went missing early Sept. 13 after she got lost in Charlottesville and ended up in the city’s Downtown Mall, outside of campus. Her body was found five weeks later on an abandoned property in Albemarle, about 12 miles from Charlottesville.

Police arrested Jesse L. Matthew Jr., 32, on Sept. 24 in Texas on charges related to her disappearance — he was seen on video surveillance footage walking with her, and witnesses saw the two together after 1 a.m. Sept. 13 — but no one has been charged in Graham’s death.

Matthew is being held in Fairfax County on separate charges of sexual assault and attempted capital murder in a 2005 Fairfax City case.

Frank Battle, an administrator in the medical examiner’s office, said Tuesday morning that investigators have made a determination of how Graham died but withheld the information at the request of law enforcement agencies. It is not rare for the medical examiner’s office to cooperate with authorities and not release details of a death investigation, Battle said.

James L. Camblos III, the lawyer representing Mathew in the Fairfax and Graham cases, said he was not surprised by the medical examiner’s report.

Hannah Graham timeline

“The findings were not unexpected,” Camblos said, noting that he was informed of the cause of death by the Albemarle prosecutor’s office.