CALGARY -- A lawyer defending two Calgary parents accused of killing their teenage son argued Wednesday they cannot be found guilty of murder.

Emil Radita, 59, and his wife, Rodica, 54, are charged with first-degree-murder in the 2013 death of 15-year-old Alexandru. They have pleaded not guilty.

The teen, who was one of eight children, weighed just 37 pounds when he died of starvation and complications from untreated diabetes.

"The only real question this court needs to answer all centres around intent," lawyer Andrea Serink, who represents Rodica Radita, said in her final argument.

"You have to be satisfied that the only conclusion is that these individuals intended to have Alex die or intended to put him in circumstances that they knew would result in his death."

Serink said in order to prove first-degree murder, the Crown would have to prove both planning and intent.

"There's no confession ... There's no evidence that Alex was being held against his will," she said.

"You would essentially have to infer that the Raditas are so malicious that they purposely planned and wanted to witness a slow and deliberate death of their son Alex."

She told court that failing to treat his diabetes is not the same as intending to murder. The judge hearing the case should only consider manslaughter or criminal negligence, she said.

"A sad and avoidable death, whether caused by irrational omission or negligence, can be characterized as culpable homicide but that does not mean it equates to murder," Serink said.

"The Crown has not proven the Raditas formed the specific intent for murder and they should be acquitted of that charge."

The trial has heard from medical officials and social workers who were involved with the Raditas from the time Alexandru was first diagnosed with diabetes in 2000 up until the family left British Columbia. They moved to Alberta while under the eye of child-welfare services.

Witnesses have testified the Raditas refused to accept that their son had diabetes and failed to treat his disease until he was hospitalized near death in 2003. One witness described the teen as nothing more than "skin and bones."

Social workers apprehended Alexandru after his October 2003 hospital admission and placed him in foster care -- where he thrived -- for nearly a year before he was returned to his family.

After the family moved to Alberta, the court was told he was enrolled in an online school program for one year but never finished. The boy never saw a doctor, although he did have an Alberta health insurance number.

On Tuesday, the victim's sister testified her brother was a "vibrant person", "very artistic, smart" who was happy "most of the time".

She said the last time she spoke to her brother was the week he died. He was staying in their parents' bedroom because "he was kind of sick ... just the daily sickness, I guess."

The young woman also acknowledged her parents did not believe in taking their children to doctors on religious grounds.

The Crown's closing argument is scheduled for Thursday.