He was acquitted by a jury of helping two men kill Bowers that night, but found guilty of robbing her. He stood by as she was beaten over the head with a meat tenderizer three times while she begged for her life, prosecutors said. The high school girl was raped and strangled.
Bowers, 16, was a student at City College. She had a crush on Rivers and prosecutors said the boy preyed on her affection, leading two men to her home.
"His role was the door through which this atrocity occurred," the judge said, "I cannot overlook that."
Rivers' attorney, Roya Hanna, said she will appeal. The boy, 14 years old on the night of the murder, would have been killed himself if he had tried to intervene, Hanna said.
John Childs, 22, and Adonay Dixon, 26, pleaded guilty to killing Bowers. Childs was sentenced to life in prison; Dixon was sentenced to 50 years. Childs admitted to beating Bowers over her head, raping and murdering her. Dixon admitted to directing the burglary plot.
"I cannot imagine, as a 14-year-old, to stand up again that," Hanna said. "I'm not sure anybody in a similar position could have done more and not been killed himself."
Bowers lived with her grandmother, who had left for work that night. The men planned to use Rivers to lure the girl upstairs while they stole from the house. But she came down and found them, prosecutors said.
"I don't recognize in this defendant any sense of human compassion," prosecutor Sharon Holback said of Rivers. "He was the key to everything that happened to Arnesha Bowers, even though the jury in their compassion or judgment convicted him only of robbery."
Baltimore State's Attorney Marilyn Mosby said in a statement she hopes the sentence brings justice for Bowers' grieving family.
"Today's sentence marks closure to an utterly brutal sexual assault and murder of an innocent, bright, and beautiful young woman," she said.
The boy's family crowded the back of the courtroom Friday, but they declined to speak. Rivers was asked if he wished to address the judge.