As Ms. Glantz read from the statement, the defendant could be seen sitting quietly in front of a video camera at the city-run juvenile center where he is being held. He pursed his lips and leaned forward occasionally, but otherwise showed little emotion.
An aunt and uncle who are the boy’s legal guardians, Shaquoya Carr and Roosevelt Davis, were visible in another video panel.
In their statement, Ms. Majors’s family questioned the point of several days of pretrial hearings — many of them attended by the defendant’s family and the victim’s father, Inman Majors — during which public defenders sought to have the teenager’s confession thrown out.
“These hearings have amplified our pain,” Ms. Glanz read from the family’s statement.
The teenager who was sentenced on Monday told the police shortly after the killing that he had taken part in the mugging that preceded it. Prosecutors originally charged him as a juvenile with second-degree felony murder. He was 13 at the time, and he pleaded not guilty.
Under state law, prosecutors have the discretion to try defendants as young as 14 as adults in certain cases of violent crime.
One of the other teenagers charged in the case, Luchiano Lewis, held Ms. Majors in a headlock and the other teenager, Rashaun Weaver stabbed her at least four times after she refused to give them her cellphone, with one thrust piercing her heart, according to prosecutors. Ms. Majors was heard yelling “Help me! I’m being robbed!,” according to court documents.
In entering his plea on June 3, the defendant sentenced on Monday described how he and his two friends had gone to the park to rob people and had zeroed in on Ms. Majors as a target as she began to climb a set of stairs.