By Rupa Shenoy | WGBH | December 1, 2015

The murder trial of 16-year-old Philip Chism case is playing out as the state and country dramatically changes the way it adjudicates juvenile crime. For the defense team, that means there are very specific things to prove as the jury decides whether Chism is or is not guilty by reason of insanity.

Prosecutors for the Commonwealth rested their case Monday against Chism, who is charged with first-degree murder with atrocity and cruelty. Chism, of Danvers, is charged as an adult in the death of his math teacher, Colleen Ritzer.

David Siegel, who represented juveniles charged as adults as a public defender, and is now director of the Center for Law and Social Responsibility at New England Law Boston, says the case stands out for two reasons.

“First, it comes after the Supreme Court has made a major change to juvenile sentencing that’s been implemented in Massachusetts,” Siegel said. “And second, because it involves some of the newest learning about juvenile decision making and juvenile brain development.”

The U.S. Supreme Court recently ruled that juveniles — even those charged as adults — can’t be automatically sentenced to life in prison.

“If this exact same crime had been committed by someone over 18, they would have an automatic sentence of life without parole,” Siegel said.

Since Chism is a juvenile, the court has discretion in how to sentence him. Siegel says the minimum sentence Chism could receive if found guilty would be 30 years in prison before being eligible for parole. And the court may be more inclined to give Chism the minimum sentence if defense attorneys can prove Ritzer didn’t suffer.

So while prosecutors told the jury that Chism acted with cold deliberation, preparing for the crime, and carrying it out cruelly, defense attorneys, in their questions to witnesses, argued that he killed Ritzer quickly, raising the idea that she didn’t suffer much — and perhaps was already dead when she was stabbed a dozen times in the throat.

“These closely clustered, basically lined-up, parallel injuries would be consistent with that scenario — that the victim was not moving,” said defense attorney John Osler as he questioned medical examiner Anna McDonald.

“That is one possiblity, yes,” McDonald replied.

“It’d be consistent,” Osler continued.

“It’s not inconsistent,” MacDonald said.

Osler went on to argue, once the jury was out of the room, that Ritzer may have been dead when she was raped, and consequently, under Massachusetts law, the rape charge should be dropped. Judge David Lowy is expected to rule on that today.

To bolster their case, defense attorneys this week are also expected to call mental health experts. Those experts will be able to make the case that Chism’s teenaged brain isn’t fully developed, and he doesn’t have the reasoning skills of an adult — even though he’s being tried as an adult. That’s because, as Siegel explains, the U.S. and Massachusetts Supreme Courts recently recognized that teenagers’ brains are still developing.

“The parts of the brain that are involved in higher order executive function, more complex decision making and mediating impulses, those parts of the brain develop last and they often don’t develop until people are in their early 20s,” Siegel said.

It’s not clear how questions about juvenile brain development fit with the crux of the defense argument — that Chism is mentally ill. Judith Edersheim, co-founder and co-director of the Center for Law, Brain and Behavior at Harvard Medical School, says it can be difficult to diagnose teens with mental illness.

“They’re not fixed. They’re developing,” Edersheim said. “And so it’s particularly tricky to diagnose children and adolescents.”

Defense attorneys contend Chism had an undiagnosed psychosis that was exacerbated when he moved from Tennessee to Danvers and started at a new school. Chism’s defense team seems to be building a case that his irrational behavior after killing Chism demonstrates his mental illness. They noted how he wandered the school halls in bloody clothes and used Ritzer’s credit cards. And Edersheim says failure to hide a crime generally indicates someone doesn’t understand what they did.

“If you sit waiting for the police to come after you, if you use your own car, sit in it with the loot you’ve stolen, you call a newspaper reporter and say, ‘Look what I did, isn’t this awesome?’ — that would be an indication that you don’t appreciate that what you did was wrong,” she said.

Edersheim says in some exceptional cases people can plan a crime — as prosecutors say Chism did — and still be found not guilty by reason of insanity. And defense mental health experts will likely argue that’s what should happen in Chism’s case. Ultimately the jury will decide if Chism’s apparent planning of his crime and seeming carelessness about it afterward mean he’s insane, or someone who intentionally acted with atrocity and cruelty.

This piece was originally published by WGBH.