Andre Butler, 18, was set to go on trial in the officer's September, 2008 death, which came at the end of a high-speed chase.
Butler, who was 16 years old at the time of the crash, pleaded guilty to third degree murder and other charges. He faces 10 to 20 years in prison.
In a brief statement in court, Butler apologized for his actions.
Nazario, a 40-year-old single mom and strike force officer, died after a stolen SUV, driven by Butler, plowed into her police cruiser at 39th and Wallace Streets.
Her longtime partner, Officer Terry Tull, drove the cruiser that night. He suffered numerous injuries.
Butler fled on foot but was captured a short time later.
Expressions of anger in the court
Family members and Officer Tull were allowed to address the court during victim impact statements.
Outside the courtroom, they made it clear how they felt about Andre Butler.
"I don't think he needs to be breathing the same air we're breathing," said Nazario's sister Maritza Mohamad.
Tull grew angry as he addressed Butler in court during impact testimony.
"Emotionally I don't know if he'll ever be the same, if he'll ever get over it. Every day it gets a little more bearable, but clearly I think you could hear from his statement that it's still something that's very much on his mind," said Commissioner Charles Ramsey.
Nazario is survived by her only daughter, 17 year old Jazmine. The teenager wept as she talked about her mother, her best friend, and the life she'll live without her.
The guilty plea spares Jazmine and her family an emotional trial.
