Ratley suffered permanent brain damage from the beating, a neurosurgeon testified at trial, and she likely will have trouble forming any new memories for the rest of her life.

The two teens had never met, but that morning Treacy received a text message from a girlfriend who had borrowed Ratley’s phone to contact him. Ratley disapproved of the relationship, though, and told Treacy so when she got her cell phone back.

The text message exchange quickly became abusive, with both teens insulting each other.

After receiving the message, Treacy replied with a threat to “strangle the life” out of Ratley, and he also broadcast his intention to commit murder in numerous text messages to friends.

Schneider told the jury those messages showed Treacy’s predisposition to commit murder — and that other text messages he sent that day telling friends he was going to prison, and leaving his belongings for others showed that he understood the consequences of his actions.

The five-day trial included testimony from about a dozen witnesses who said they saw Treacy savagely beat Ratley at the bus stop of the middle school shortly after classes had ended for the day.

The prosecution had also presented a witness who testified that someone using Treacy’s computer profile had searched Google the night before the attack using the terms “how to commit murder’’ and “how to kill someone.’’

Also testifying were two psychiatrists — one for the prosecution; the other for the defense — who diagnosed Treacy with post-traumatic stress disorder and depression stemming from his having witnessed the suicide of his older brother.

But the psychiatrists differed over the details of exactly when Treacy first experienced a dissociative episode, the severity of the disorder, and perhaps most importantly for Treacy’s fate, whether he was conscious of his actions and their consequences.

Williams, the defense attorney, urged jurors during closing arguments last week to find Treacy not guilty by reason of insanity.

“At the time of the episode he was legally insane,’’ Williams said.

But Schneider argued that Treacy knew what he was doing, and that he was motivated by anger.

“Anger does not equate insanity,’’ she told jurors. “Viciousness is not a mental illness.’’

After Monday’s verdict, Schneider told reporters that Ratley’s family wanted Treacy to serve 30 years in prison for his crime, but that the sentence to be imposed by the judge likely will not be an easy one to determine.

“It’s difficult,’’ she said, “to put a number on anyone’s life.’’

Judge Haimes said he will sentence Treacy within 90 days, after a pre-sentencing investigation. He scheduled a status conference for Aug. 29.