iStock/Thinkstock(CAMBRIDGE, Mass.) — A 15-year-old girl has died after she was shoved to the ground in a mysterious assault in Cambridge, Massachusetts, prosecutors said.

Now investigators are looking for answers.

The 15-year-old girl was “walking to an acquaintance’s house” in Cambridge at about 6:30 p.m. Sunday when she was thrown to the ground, hitting her head, the Middlesex District Attorney’s Office said.

She was hospitalized in critical condition and died Monday afternoon, according to prosecutors.

Her name was not released by officials, but she was a student at Cambridge Rindge and Latin School, according to ABC affiliate WCVB-TV in Boston.

“Our community is devastated to learn that one of our students has passed away following an incident on Sunday night,” Cambridge Public Schools Superintendent Kenneth Salim said in a statement Tuesday. “Words cannot express the depth of our sorrow for this loss.”

No arrests have been made, but investigators are trying to find any witnesses, including “information concerning the identity of a person seen in the area on a bicycle,” the district attorney’s office said Tuesday.

The district attorney’s office would not comment on a potential motive.

Prosecutors are still awaiting a cause and manner of death from the medical examiner’s office, the district attorney’s office said.

Anyone who may have information is asked to call the Massachusetts State Police assigned to the Middlesex District Attorney’s Office at (781) 897-6600.

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