(Reuters) - A Massachusetts man armed with a hunting knife stabbed a 22-year-old woman to death at a public library in an unprovoked attack on Saturday and wounded a man who tried to come to her aid, a prosecutor said.

The suspect, Jeffery Yao, 23, of Winchester, approached the woman and stabbed her multiple times with a 10-inch hunting knife at a library reading room table, Middlesex County District Attorney Marian Ryan said at a news conference.

The woman, a resident of Winchester, a Boston suburb, was slashed and stabbed in the upper torso and head and died at a hospital. A 77-year-old Winchester man who tried to intervene was stabbed in the arm but not seriously hurt, Ryan said.

Police arrested Yao at the library. He was charged with murder and assault and jailed without bail pending arraignment on Monday. It was not immediately clear if he had an attorney.

Police are seeking a motive in the attack. The slain woman has not been identified pending notification of relatives.

The library said on its Twitter feed that it would remain closed until Monday afternoon.