It took five days, but a jury was seated in her case Wednesday.
Dozens of potential jurors were screened one-by-one --highly unusual for an arson case-- and let go, because many of the potential jurors already knew her as the woman who falsely accused several Duke Lacrosse players of rape in 2006.
The jury will have to decide if Magnum is guilty of felony first degree arson.
Police say back in February she punched and scratched her then-boyfriend Milton Walker, threw his clothes in a tub and set them on fire, all while her three kids and police were in the house.
The first officers who responded to the domestic violence call took the witness stand Thursday and both officers said Mangum wasn't cooperative.
"I believe she said that they were arguing and after, I think I asked her another question and I just got silence," Durham Police officer Hillary Thompson said. "She refused to answer any other questions. She really wasn't cooperating with us. The children seemed okay so there was nothing more we could do."
Mangum is also charged with three counts of contributing to the delinquency of a minor, injury to personal property and resisting a public officer.
Thompson testified when Mangum's boyfriend showed up at the home scratched and half naked, he was brought into the house and Mangum snapped.
"She said I'm going to stab you ...," Thompson said.
But during opening statements Thursday, Mangum's attorney told a jury Mangum was calm.
"She's trying to talk to Crystal," defense attorney Mani Dexter said. "She asks Crystal do you need help? She says she had a fight with her boyfriend and says please leave."
Her attorney said officers should have kept Mangum and her boyfriend separated.
During his opening statement, Prosecutor Mike McCullough indicated Mangum knew what she was doing that night.
"She threatened her boyfriend, didn't tell anyone she set fire," he said. "Police had to restrain her and arrest her to keep her from doing it, while there was a fire with all those people in it."
The second officer on the scene also started testified Thursday and is expected to continue Friday morning.