A middle school student from Yonkers, NY is being accused of murdering an 18 year old girl.

Police are on a man-hunt, or a boy-hunt, for an 8th grader who they claim shot an innocent bystander who pushed her younger sister out of the way of the bullets. 

Marilyn Cotto Montanez, 18, was shot and killed as she walking to a corner store bodega with her 9-year-old sister yesterday. Police believe that she was caught in the crossfire of a shooting.

Marilyn, who is a high school junior, saved her sister's life, by shielding her from the incoming bullets, and then pushing the child to safety.

Police believe that the shooter is 15-year-old Jamir Thompson, who is currently in middle school.

According to authorities, Jamir was aiming at a rival in a dispute over a stolen gold chain. Sources say the two rivals were arguing and the argument escalated to gunshots.

Jamir was ID'd as the shooter after police canvassed the neighborhood for leads in the case. Police believe he may have fled the Yonkers area. 

The Yonkers Police Department is offering a $5,000 reward for information leading to his arrest.

Hours before Marilyn Cotto Montanez was killed Thursday she sat in her principal's office revising her school schedule for her coming senior year at Lincoln High School. Her classes, she complained, were too easy.

"This is not good enough for me," she told Principal Ian Sherman. "I have bigger plans and I want to go to college."

Teachers, administrators and classmates who knew Montanez described her as a quiet, determined student with a relentless work-ethic for whom scores like 99 and 100 were the rule rather than the exception.

"She never shied away from what was hard," Sherman said. "She knew she deserved more and she did everything she could to get more."

Rest in peace, Marilyn, out thoughts and prayers are with her family.