Prosecutors said they have DNA evidence placing Johnson at the scene.
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The jury deliberated for only two hours.
After the verdict was read Wednesday, Johnson collapsed in court and had to be held up by deputies.
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Prosecutors told the jury that Johnson stalked Pierce mistakenly thinking Pierce was having an affair with her estranged husband.
"I'm thankful for the family of the victim that this will be another step in closure for them and they can get on healing,” Rowan County Sheriff Kevin Auten said.
The judge told Johnson she'd die in prison and sentenced her to life without parole.