A Massachusetts teenager has been convicted of raping and killing his high school math teacher. Philip Chism was convicted Tuesday in the 2013 slaying of Colleen Ritzer, a 24-year-old algebra teacher at Danvers High School, about 25 miles north of Boston. Chism's lawyer admitted his client killed Ritzer, but said he was suffering from severe mental illness and wasn't criminally responsible for his actions. 

3:58

A jury has reached a verdict in the trial of a Massachusetts teen who killed his math teacher in 2013.

The jury in the trial of Philip Chism deliberated for about 10 hours Monday and Tuesday before telling the judge it has reached its decision.

Chism is charged with raping and killing Colleen Ritzer, his 24-year-old algebra teacher at Danvers High School.

His lawyers admitted Chism killed Ritzer, but have asked the jury to find him not guilty by reason of insanity.

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2:30 p.m.

Jurors in the trial of a Massachusetts teen who killed his math teacher have received additional instructions from the judge on aggravated rape charges against him.

Philip Chism is charged with raping and killing Colleen Ritzer in 2013. His lawyers admit he killed Ritzer, but say he was severely mentally ill and have asked the jury to find him not guilty by reason of insanity.

Jurors began deliberating Monday. On Tuesday, they asked the judge to clarify the aggravated rape charges. Chism is accused of raping Ritzer once inside a girl's bathroom at Danvers High School and then violating her with a tree branch in woods near the school, where he put her body.

Judge David Lowy told the jury that to find Chism guilty of the rape in the woods, prosecutors must prove that the rape and Ritzer's death happened in close proximity.

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9:30 a.m.

The jury in the trial of a Massachusetts teen who killed his math teacher have resumed deliberations on murder and aggravated rape charges.

Jurors deliberated a little over three hours Monday in the trial of Philip Chism, charged in the 2013 killing of Colleen Ritzer, his algebra teacher at Danvers High School. The jury resumed deliberations Tuesday morning.

Chism's lawyers admit he killed Ritzer, but say he was severely mentally ill and cannot be held criminally responsible for his actions.

Prosecutors say Chism knew right from wrong and plotted to kill the 24-year-old Ritzer, bringing a box cutter, gloves and other items to school.

Chism was 14 at the time. He is now 16 and is being tried as an adult.

Earlier from WGBH News:

Three weeks after they began hearing testimony, the jurors in the Philip Chism murder trial have retired to deliberate his fate.

Chism’s lawyers admitted that when he was 14 years old he killed and raped his high school math teacher.

Lawyers for the prosecution and defense portrayed Chism in terms that were worlds apart.

Defense attorney Denise Regan said Chism’s crime only makes sense if he was mentally ill. Regan said Chism lost his support system when he moved to Massachusetts from Tennessee. She also brought up his race for the first time in the proceedings, suggesting that his mixed parentage added to his isolation.

“He was an unusually tall African American boy in a predominantly white school who had no place to hide,” said Regan.

In closing, Assistant District Attorney Kate MacDougall at one point gripped the boxcutter Chism used to cut Colleen Ritzer’s throat.

“He had a goal,” said MacDougall. “A terrible, terrible purpose. And he played it out in the woods. And he didn’t care what came after that.”

MacDougall told jurors Chism never heard voices because he had been faking his mental illness from the beginning. She said Chism knew what he was doing was wrong when he killed and raped Ritzer.

Previously from The Associated Press (1:25 p.m.)

Jurors have begun deliberations in the trial of a Massachusetts teenager who raped and killed his high school math teacher.

A prosecutor says Philip Chism "knew right from wrong and could choose right from wrong."

But a defense attorney says the then-14-year-old Chism was in "the throes of mental illness" when he killed 24-year-old Colleen Ritzer in 2013, shortly after he moved to Massachusetts from Clarksville, Tennessee.

Prosecutors say Chism strangled Ritzer and stabbed her with a box cutter in a Danvers High School bathroom, then used a trash bin to bring her body into nearby woods.

Assistant District Attorney Kate MacDougall told the jurors that doing something awful doesn't make you crazy.

Defense attorney Denise Regan said jurors must be certain beyond a reasonable doubt that Chism wasn't mentally ill.

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11:25 a.m.

A prosecutor in the trial of a Massachusetts teenager charged with raping and killing his high school math teacher says Philip Chism "knew right from wrong and could choose right from wrong."

But a defense attorney says the then 14-year-old Chism was in "the throes of mental illness" when he killed 24-year-old Colleen Ritzer in 2013.

Jurors could begin deliberations later Monday after hearing closing arguments from both sides.

Prosecutors say Chism strangled Ritzer and stabbed her with a box cutter in a Danvers High School bathroom, then used a trash bin to bring her body into nearby woods.

Assistant District Attorney Kate MacDougall told the jurors that doing something awful doesn't make you crazy.

Defense attorney Denise Regan said jurors must be certain beyond a reasonable doubt that Chism wasn't mentally ill.

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