During the opening of jury selection in Essex Superior Court in Salem, Judge David A. Lowy told potential jurors that they may be asked questions about their views on criminal responsibility and insanity.
Prosecutors say Chism, then 14, strangled his math teacher, Colleen Ritzer, in a school bathroom on the afternoon of Oct. 22, 2013, slit her throat, and left her with 16 stab wounds.
The freshman then, police contend, put her in a recycling bin and dragged it into the woods near the school, where her half-naked body was found early on Oct. 23, 2013.
Prosecutors say Chism left a folded, handwritten note near her that read: “I hate you all.”
He is also accused of sexually assaulting Ritzer, 24, and stealing her underwear and credit cards.
Chism, now 16, is charged as an adult with first-degree murder and is being tried as a youthful offender on two counts of aggravated rape and one count of armed robbery. He has pleaded not guilty.
Prosecutors say Chism confessed to the crimes, but a judge ruled that jurors won’t hear the statements police said he made.
On Wednesday, defense attorney Denise Regan introduced Chism to prospective jurors and referred to him as “the juvenile.” Chism did not speak.
If Chism’s lawyers mount a defense on the grounds that he was not criminally responsible, Lowy said the burden is on prosecutors to prove beyond a reasonable doubt that the teenager was not insane.
To do this, Lowy said, prosecutors must show that Chism did not suffer from a mental disease or defect. If he did have such an illness, it’s up to the prosecution to demonstrate that Chism still knew right from wrong and could conform his behavior to the law.
Adult defendants who are found not guilty by reason of insanity are evaluated at a facility for 40 days and subject to possible commitment, Lowy said.
The defense notified the court in July that it would offer testimony about Chism’s mental state from an expert witness, but the lawyers have not explicitly declared their intention to use the insanity defense.
The expert witness is identified in court papers as Dr. Richard G. Dudley Jr., a New York City psychiatrist who evaluated Colin Ferguson, the gunman who killed six people on a Long Island commuter train in 1993.
Attorney Randy Chapman, who is not associated with the Chism case, said potential jurors are probably being asked about insanity and criminal responsibility to determine whether they would consider such a defense.
“If a potential juror were to get on and say ‘I don’t believe anybody should ever be excused for reason of insanity,’ this person would not be able to sit on this jury because they can’t be fair and impartial and apply the law,” said Chapman, former president of the Massachusetts Association of Criminal Defense Lawyers.
Lowy, defense lawyers, and prosecutors met with 115 potential jurors Wednesday and asked whether they knew any of the possible witnesses or if serving on the trial would cause a hardship. Lowy dismissed 56 of the prospective jurors.
John R. Ellement of the Globe staff contributed to this report. Laura Crimaldi can be reached at firstname.lastname@example.org.