A man armed with a hunting knife stabbed a woman to death Saturday inside a public library in Massachusetts, authorities said.

When police arrived, they found that an elderly man also had been stabbed, Boston's Fox 25 reported.

"There were three to four police cars here, there was an ambulance and there was a woman taken out," Russ Ganz, a Winchester resident, told the station.

The suspect -- identified as Jeffrey Yao, 23 -- allegedly approached the 22-year-old woman from behind as she was seated at a table in the reading room of Winchester Public Library, Middlesex District Attorney Marian Ryan said.

The blade was said to be 10 inches long and the suspect reportedly stabbed the woman multiple times.

During the attack, the young woman suffered injuries to her head and upper torso, Ryan said. As she struggled toward the door, onlookers reportedly tried to help her escape.

A 77-year-old man who tried to help the woman was also injured in the attack, suffering a non-life-threatening stab wound to an arm, Ryan said.

Authorities have opened an investigation into the attack and were working to determine a motive, a news release from the district attorney’s office said.

It wasn’t clear if Yao knew the woman, but the suspect was “known to police,” Ryan said. The woman’s identity was being withheld until her family could be notified, she added.

The suspect was charged with murder and armed assault with intent to murder, the news release said. He was being held without bail and was expected to appear in court Monday.

The Associated Press contributed to this report.