Pat Dollins/Mountain Democrat/Zuma
06/14/2011 AT 07:35 PM EDT
A Northern California jury that heard closing arguments Tuesday is faced with the question of who brutally killled a 47-year-old mother: Her rebellious 14-year-old daughter or the daughter's older boyfriend.
On the witness stand over the past two weeks, Joanne Witt's daughter Tylar, now 16, and Tylar's former boyfriend, Steven "Boston" Colver, 21, blamed each other for the slaying two years ago in the Witts' upscale El Dorado Hills, Calif., home.
Prosecutor Lisette Suder told jurors that the logical conclusion is that it was Colver who stabbed Joanne Witt 20 times and slashed her throat.
"A 14-year-old girl did not do this to her mother," said Suder, who pointed to what the prosecution has called compelling physical evidence: male DNA found under the victim's fingernails.
Colver alone is on trial because Tylar took a plea deal
last year, admitting to a first-degree murder charge that could be reduced to second-degree murder, making her eligible for parole before age 30, in exchange for her testimony.
Colver took the stand in his defense and pinned the blame on Tylar – saying that she called him to come over, then confessed to the murder.
"She was holding a kitchen knife and there was a red stain on her right pant leg. I was shocked," Colver testified. "She said, ‘Boston, I did it. I finally did it. My mom's gone forever.’
"I asked, ‘What the hell did you do?’ She said, ‘I did the only thing I could do.’ She collapsed into my arms, saying she did it for us."
He testified he didn’t call police because "our plan was to die together."
In her testimony a week earlier, Tylar said she couldn’t even bring herself to enter the room as her mother was stabbed.
"I couldn't do it. I couldn't go inside," she said. "I put my hands over my ears, closed my eyes, and hummed."