AMHERST —A 20-year-old Wayland man died after a fall from a retaining wall off Fearing Street early on the morning of Sept. 16, according to the Northwestern district attorney’s office.

The man’s death is being investigated by the Amherst police, working with the Massachusetts State Police Detectives Unit assigned to the Northwestern district attorney’s office.

Witnesses told police that the man, who was not a University of Massachusetts student, had attended a party on North Pleasant Street during the evening and then ran into a yard behind a residence on Fearing Street around 2:30 a.m., Mary Carey, a spokeswoman in the DA’s office, wrote in a statement.

There, Carey said, investigators believe the man fell from a 10-foot retaining wall and struck his head upon landing in a shallow brook.

Amherst Fire Department paramedics and Amherst police officers responded to a 911 call for the injured man, who was unresponsive and had injuries to his head, according to Carey.

The man was transported by ambulance to Cooley Dickinson Hospital, where he was pronounced dead.

The Office of the Chief Medical Examiner has not pronounced the cause of death, and toxicology results are pending. The death does not appear to be criminal in nature, Carey said.

Investigators are trying to determine the man’s whereabouts and activities in the hours preceding his death, in addition to the party on North Pleasant, Carey said.

The incident marked the second death in five years on the street, a busy pedestrian walkway late at night during the academic year. In November 2012, a female student died after an accidental fall on the street.

UMass spokesman Daniel Fitzgibbons stated in an email that, while the victim in Saturday’s incident was not a student, officials are ready to provide support to anyone affected by his death.

“If students are affected by the death of family members, friends, etc., the university offers referrals to the Center for Counseling and Psychological Health and notifies faculty members so that they are aware of the situation and can make appropriate accommodations,” Fitzibbons wrote.