Calls about a possible active shooter at Howard University on Tuesday that drew a large police response came after a student’s ex-boyfriend repeatedly threatened her and warned her about being on campus, according to law enforcement officials and court documents.

Police found no gun and no shooter and said they were looking into the alleged threats. Several officials said the man had been rejected for the university’s medical program and barred from the Northwest Washington campus two weeks ago. They believe the calls about a shooter were made by people concerned about the young woman’s safety and fueled by false rumors.

The ex-girlfriend had obtained a temporary protection order against the man and said in her court petition that he told her, “Do not go to campus” and “there are those that will see you hurt more than words.” She wrote that he warned her that “going to police is unacceptable” and that he knew she had an exam Tuesday and that he would be there. Police said the young man was not in custody but was being investigated.

The shooting scare came during the run-up to Howard’s homecoming celebration this weekend and the anticipated visit by thousands of graduates and others for activities at the historically black college founded in 1867.

D.C. police reacted swiftly to the emergency calls, sending more than 100 officers, many armed with semiautomatic rifles. They searched three campus buildings, closed streets and put the campus under lockdown for two hours. Classes were canceled for the day.

“We have found no evidence that supports there was a shooting on our campus,” Howard’s interim police chief, Alonzo F. Joy Jr., told reporters after the all-clear was given. He warned of “some serious repercussions if we identify” a person responsible for the incident, but he declined to discuss specifics.

Students interviewed said there had been rumors about a disturbance on campus Tuesday. Danea Rutherford, 19, said she and her friends did not take it seriously because Howard officials had not warned of any threats. They were in a classroom in a campus building when they saw police cars.

“It was scary,” she said. “We kept on hearing the dogs, we kept on seeing police running.”

Rutherford said she saw police long before she received an alert from the university.

While she and others barricaded the classroom door, someone was trying to get inside the room, said Rutherford, a sophomore at Howard. They didn’t immediately realize it was a Howard official.

“We were on the phone with our parents, and everyone just stopped and looked at the door,” she said. “I couldn’t move. I was like, ‘We get shot today, I don’t know what to say.’ ”

The incident began to unfold shortly before noon at the university, which is off Georgia and Michigan avenues. Joy said the first call to campus police reported a shooting at the College of Medicine building near the 2400 block of Sixth Street NW. Campus officers reported that they did not hear any gunshots but began to search the floors.

At 12:02 p.m., another call — this one anonymous — reporting a shooting at Howard’s administrative building came in to the District’s 911 center, the Office of Unified Communication. Officials said it was the first of five separate 911 calls reporting a shooting.

Howard University’s student newspaper, the Hilltop, posted an image of the school’s alerts on Twitter. According to the tweet, at 12:42 p.m., a message went out reading: “ALERT!! There is a report of an ARMED person throughout the campus shelter in place while police investigate.”

Asked if police notified students quickly enough, the university’s president, Wayne A.I. Frederick, said, “I think that we were doing the best we could with the limited information we had.”

Officials said they had not determined the genesis of the calls. Two law enforcement officials said some or all may have come from the ex-girlfriend’s worried friends or relatives, and they are exploring whether allegations about a shooting circulated on social media before the calls to police were made.

The officials said all the calls were from people who believed a shooting had occurred. The officials said D.C. police did not know about the prior threats before they responded.

Police searched the medicine building and an attached annex, the administrative building, and a third office. The alert was lifted at 2:05 p.m.

The ex-girlfriend had filed for the protective order in D.C. Superior Court on Friday. She detailed several days of alleged abuse, along with threatening emails. She wrote that among those threatened were her cat and relatives, and she said her former boyfriend told her he had secretly installed cameras in her campus residence.

The woman said in the petition that she saw the man on campus Sept. 29 and “felt uncomfortable.”

Dana Hedgpeth contributed to this report.