CASTLETON, Vt. (AP) — Students at a Vermont university returned to classes Tuesday, some on edge, as police continued to search for the killer of a retired dean who was shot last week while walking on a recreational trail near campus in the small town.

Honoree Fleming, a retired dean and professor, was found shot to death on Thursday afternoon on the Delaware & Hudson Rail Trail about a mile (1.61 kilometers) south of the Castleton campus of Vermont State University. The shooting happened during the school’s week-long fall break. The university reopened Monday but students were excused from classes.

“I recommend to the public to be vigilant, have some awareness,” Maj. Dan Trudeau, commander of the Vermont State Police’s criminal division, said Monday. “If you’re out be with a friend because we don’t really know yet if the community is in any further danger. We don’t know if this is isolated or not isolated and we’re still trying to develop leads to further figure that out.”

A witness reported a possible suspect was northbound on the trail walking towards the campus after gunshots were heard, police said. The witness described a 5-foot-10-inch (1.78-meter) white male with short, red hair, last seen wearing a dark gray T-shirt and carrying a black backpack. State police said he is considered to be armed and dangerous and asked anyone who might have seen him to call them.

Castleton Police Chief Peter Mantello said they don’t know if this was a random or targeted shooting and advised residents of the town of about 1,200 and students to be diligent by locking their cars and doors.

While the university boosted security on campus and advises students to travel in groups and lock their doors, some students said they wished classes would continue to be cancelled while the investigation is ongoing.

“I was hoping that they would extend their break, trying to figure out if they can try and catch this guy, just so I could feel more safe,” sophomore Jasmine Traverse told mynbc5.

Other students said they feel safe because of what the university is doing.

“I do feel safe, not necessarily on the trail at this moment, but in general on campus, I do feel safe,” Pearl Bellomo told WCAX-TV.

Vermont State Police said they have received more than 200 tips as they search for the killer.

Detectives have been interviewing nearby residents and people who were on the trail around the time of the shooting, police said. The Vermont State Police canvassed the trail on Monday looking for any additional evidence, authorities said.

“Please, as far as the public goes, provides us tips,” Trudeau said. “Anything noteworthy that you found on cameras, something maybe you drove by and noticed and thought of after the fact. We’re primarily interested in anyone who was walking on the rail trail that day ... in the timeframe of 3 p.m. to 5 p.m.”

The Castleton campus of Vermont State University cancelled classes on Monday to ensure that the school community “has the time and space to process and grieve.”

“Following the tragic death of a member of our community in Castleton on Thursday, we want to express our deepest condolences to all members of our community who knew and were touched by Dr. Honoree Fleming,” the school said in a Facebook post. “Her contributions to education and her impact on our campus will live on in all of us.”

Fleming was married to author Ron Powers, who co-wrote the book “Flags of Our Fathers,” about the men involved in the famous flag-raising during the 1945 Battle of Iwo Jima. A Pulitzer Prize winner in 1973 for criticism as a television-radio columnist, he also wrote a biography of Mark Twain and collaborated with the late U.S. Sen. Edward Kennedy on the politician’s memoir, “True Compass.”