WOBURN (CBS) – Isaias Plaza been charged with manslaughter in the 2018 death of 15-year-old Richelle Robinson, who died after being shoved and hitting her head on a Cambridge sidewalk.

Richelle Robinson died in July 2018 when police say she was thrown to the ground on Cambridge Street. Robinson was rushed to the hospital but did not survive.

“First responders saw that she had blood coming from her nose and from the back of her head. She was unresponsive, did not have a pulse, and did not appear to be breathing,” Assistant District Attorney Nicole Allain.

During his arraignment Tuesday in Middlesex Superior Court, Plaza, 19, pleaded not guilty to charges of manslaughter and assault and battery with serious bodily injury.

Prosecutors say there is video showing Plaza riding his bicycle near Robinson the day she was killed. He denied being involved in Robinson’s death, but prosecutors said Plaza told someone he accidentally pushed her.

Plaza had a falling out with Robinson and her friends in the weeks before the attack, prosecutors said. Plaza allegedly burned his shoes and clothes after the incident.

Robinson’s family sat in court wearing pins with her picture and the phrase “Live life to the fullest.” The family had no comment as they left the court. Cambridge Police tweeted out their condolences to Robinson’s family, calling her case “deeply personal.”

This was a case that was deeply personal for many of our Officers, as Richelle was a well-liked person who had a direct connection with the Department, as she had participated and graduated from the #CambMA Youth Police Academy Class 2 summers ago and had aspired to be an EMT. — Cambridge Police👮🏽 (@CambridgePolice) July 30, 2019

Robinson was a Cambridge Rindge and Latin student described by her family as “a very smart young lady, and very responsible.”

Plaza is being held without bail pending a dangerousness hearing.