Martzen's defense team wants the jury to believe Ella VanLeeuwen was already dying when she came to Megan's house in February 2009.
But the prosecutor got the last word with jurors, saying the only reasonable conclusion is that Megan murdered Ella. The tension of a month-long trial showed on Megan Martzen's face Friday as the case reached its conclusion.
The prosecutor painted Martzen as a teenager who was good with kids until she snapped and killed Ella VanLeeuwen with at least two blows -- to the head and the stomach.
Opening and closing with the same picture of the 17-month-old, he told the jury the defendant's explanation of what happened just didn't make sense, and there's no one who backs it up except the defendant herself.
He picked apart her testimony, pointing out perceived lies and inconsistencies -- a critical piece of closing arguments, according to attorney Charles Magill.
"When the credibility of the defendant is the most important thing they can deal with, the jury is going to look very particularly at small details that are inconsistent or improper," he said.
Martzen's defense revolves around a prior fall.
The VanLeeuwens deny it ever happened.
But medical experts testified that the pressure in Ella's head was very likely building up for several hours before she was hospitalized.
That could back up Martzen's claim that Ella's parents told her the toddler had been pushed over in a booster seat by her brother.
Magill says it could be enough to create reasonable doubt in a jury with a tough decision ahead.
"There's an innocent life that's been lost and everybody wants somebody to pay for it and sometimes accidents happen and how do you distinguish between an accident versus intentional conduct," he said. The jury got the case so late Friday, they won't start deliberating until Monday.
The attorneys can now relax after four weeks of trial. But it's definitely a stressful time now for the VanLeeuwens and for Megan Martzen, who could be free or facing a life sentence by next week.