A Middlesex County grand jury is investigating a suspect in the March 9 rape of a Harvard-affiliated woman in Byerly Hall, Harvard University Police Department (HUPD) sources confirmed yesterday.

"Evidence was presented to the grand jury, including... identification of the suspect," said a source in the police department.

Investigators said they knew from the beginning that the case would be tough to crack because the victim, whom HUPD has not identified, is reluctant to press charges.

But after several weeks of investigation-which included a line-up of potential suspects-HUPD sources said they felt they had gathered enough evidence to bring to the Middlesex County District Attorney, Martha Coakley.

Anson Kaye, a spokesperson for Coakley, said he could not confirm nor clearing the Byrely rape, citing the confidentiality of the proceedings.

Generally, he said, grand juries have three months to investigate a case before their findings are made public.

"The grand jury is often used as a tool to get information that has subpoena power," Kaye said. Twelve grand jurors out of a possible 23 are needed to "move the case forward" or issue an indictment, Kaye said.

HUPD officials would not say who the suspect is and declined to say who identified the suspect.

Police sources also said the department is attempting both to preserve the victim's right to privacy while still protecting public safety.

HUPD spokesperson Peggy A. McNamara declined to comment yesterday on the department's release of information to the district attorney's office.

"The investigation is definitely ongoing," she said.

Two days after the attack, HUPD investigators released a composite sketch of the suspect, but would not say whether the victim or a witness to the crime had given information to the sketch artist.

The suspect, a white male, is about six feet tall and 35 to 40 years old. He has very short hair, a thin build and a thin acne-scarred face.

Byerly Hall houses several offices in Harvard's Faculty of Arts and Sciences, including the undergraduate and graduate offices of admissions and financial aid, as well as administrative staff offices for the Graduate School of Arts and Sciences.

The assault occurred on the second floor of the building just after 7:15 p.m., when most employees had left for the day-and just minutes after hundreds of students held a demonstration in the Yard demanding that the University take a tough stand on sexual assault.