The teenage boy is charged with a rarely used law that allows the state to charge a person with murder for providing drugs that kill someone else.
Authorities said 16-year-old Erica Hicks died of a lethal combination of drugs that included meth, cocaine and Ecstacy.
Defense attorneys contend Hicks was a habitual drug user with multiple sources. One of their final witnesses Friday was toxicologist Dr. Donald Hoffman, who testified that with different drugs in Hicks' system, it's impossible to determine which one killed her.
"If someone uses these agents and in addition have excessive water, it can exacerbate the action of the drug," said Hoffman.
However, state toxicologist Dr. Ruth Winecker contended the excessive water consumption was associated with the Ecstacy. That's in keeping with the prosecution's case that the accused teen gave Hicks the Ecstacy that created a deadly mixture.
"It's been shown (that with) the use of Ecstacy...people drink excessive water, which results in hyponatremia and then death," said Winecker.
Closing arguments in the case are expected Monday. The judge will then take it under advisement and issue a ruling.
If the teen is convicted, he would be held until he's 21, because he's being tried as a juvenile.