WATERTOWN, Mass. (AP) — A tense night of police activity just days after the Boston Marathon bombings has caused police to converge on a neighborhood outside Boston where they say there were explosives.

The chaos in Watertown, about 10 miles west of Boston, occurred just hours after a Massachusetts Institute of Technology police officer was shot and killed on campus. It was unclear if the outbursts of violence were related. No arrests had been made in the officer’s fatal shooting, and a manhunt was on for the shooter.

The officer had been responding to report of a disturbance Thursday night when he was shot multiple times, according to a statement from the Middlesex district attorney’s office and Cambridge police. It said there were no other victims.

Meanwhile, in Watertown, witnesses reported hearing multiple gunshots and explosions at about 1 a.m. Friday. Dozens of police officers and FBI agents were in the neighborhood and a helicopter circled overhead.

State police spokesman David Procopio said, “The incident in Watertown did involve what we believe to be explosive devices possibly, potentially, being used against the police officers.”

MIT said right after the 10:30 p.m. shooting that police were sweeping the campus in Cambridge and urged people to remain indoors. They urged people urged to stay away from the Stata Building, a mixed-use building with faculty offices, classrooms and a common area.

Hours later, MIT, which has about 11,000 students, said the campus was clear but the shooter was still on the loose.