Lois Cannady, 89, was shot to death in her home more than two years ago. Prosecutors say Sullivan, who was just 16 at the time, and four other men broke into Cannady's house to steal her car.
Prosecutors believe Sullivan shot her with an assault rifle.
Lois Cannady's son, David, was allowed to address Sullivan after the verdict was read.
"The night you killed my mother, you didn't just take her life. You took my life, my brother's life, my son's life. A lot of people loved that woman," he said.
Sullivan was sentenced to life in prison. Some of Sullivan's family members were ordered to leave the courtroom Monday after they broke down in tears.
Two other co-defendants are scheduled to be tried in the case, including Gregory Lee, who was Cannady's neighbor. His trial is scheduled to begin in December.
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