Jeffrey Yao was arrested for the brutal murder of 22-year-old Deane Kenny Stryker inside the Winchester Public Library on Saturday.
Police say Yao came up behind Kenny Stryker sitting in the reading room and began stabbing her with a 10-inch hunting knife. The first year medical student was stabbed 20 times.
Yao's arrest for the fatal stabbing was not his first interaction with police.
Last September, Yao was charged with trying to break into a neighbor's house by slamming his body against a sliding glass door.
According to the report from the Winchester Police Department, they had already had several encounters with Yao.
The responding officer said, "on each of my dealings...he has displayed erratic behavior and mental instability."
Many are wondering, was the ball dropped?
Attorney Peter Eliken says, "it's really too early to pass judgment on that but it definitely should be looked into."
When Yao was being booked, officers asked if he was suicidal and he told them he felt like he was going to hurt himself.
"So that's a danger to himself."
Eliken says the threat to hurt himself could have been enough for police to ask a judge to have Yao "sectioned" or committed to a hospital for a psychiatric evaluation.
Instead, they released him into the custody of his mother, who posted $40 bail and took him to a local hospital.
At Yao's arraignment the next day, the court put him on pretrial probation for a year with the condition that he continue mental health treatment.
Often those cases are dismissed if the defendant doesn't get into trouble in that year.
"It's about as mild as handling of the situation as they could possibly do... they realized that there was some kind of mental health issue there and they wanted to see if he could benefit from treatment. Obviously we learn in hindsight that the issue was so much more extreme and serious."