WINCHESTER, Mass. (AP) — A man attacked a woman from behind at a public library near Boston on Saturday and stabbed her repeatedly with a hunting knife, killing her and injuring an elderly man who came to her aid, authorities said.

Middlesex District Attorney Marian Ryan said the 22-year-old woman was studying or doing work at a table in the Winchester Public Library's reading room when 23-year-old Jeffrey Yao attacked her with a 10-inch knife. The woman suffered numerous slash and stab wounds to her head and upper torso, Ryan said.

Ryan said the woman staggered toward the door and several people tried to help her, including a 77-year-old man who also was stabbed. The man, who was stabbed in the arm, is expected to survive, Ryan said.

The district attorney said authorities are working to determine a possible motive and whether Yao and the woman knew each other. Ryan said Yao was "known to police," but declined to elaborate.

Yao is charged with murder and armed assault with intent to murder and is being held without bail until he appears in court on Monday. A phone number for him could not be found and it was not immediately clear whether he had an attorney.

Ryan said the woman's identity is being withheld pending notification of next of kin.

Russ Ganz told The Boston Globe that he was walking by around 11 a.m. when he saw a woman being taken out of the library on a stretcher. Ganz said the woman, who was conscious, appeared to have injuries to her shoulder.

"I thought somebody fell down the stairs," he told the newspaper.