A MA 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.
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.
Police said Yao also injured a 72-year-old man when he tried jumped in and help Stryker.
She suffered multiple stab wounds to the head and upper torso and was taken to the hospital where she was pronounced dead.
The woman's name remains withheld until confirmation from next of kin. The female victim subsequently died from her injuries.
A day after the attack, one large question still loomed over the sudden burst of violence that shattered the tranquility of the town's library: Why?
Neighbours of Yao interviewed by the Boston Herald said his behaviour had become increasingly erratic in recent years.
Police are still investigating the killing.
One neighbour, a father of two young children who asked the newspaper not to use his name, said Yao had tried to "smash our door down" in a 3am incident previous year.
"They are a remarkable family", Brad Harrington said.
According to Fox News, police have been warned about Yao in the past.
The library is closed indefinitely.
Yao is being held without bail.
It wasn't clear if Yao knew the woman, but the suspect was "known to police", Ryan said.