McCarthy Hall, the dormitory where a student made ricin, is seen on the Georgetown University campus. (Katherine Frey/The Washington Post)

In the wee hours of March 18, Georgetown University Police Chief Jay Gruber faced a question as authorities responded to a report that the deadly biological toxin ricin was possibly present in McCarthy Hall.

Should the dormitory’s 290 residents be evacuated?

Gruber’s decision to leave the students in place offers a case study in the complexities of threat assessment, emergency notification and campus safety in an era when campus police everywhere are on the lookout for emergencies involving guns, extreme weather, gas leaks and even terrorism.

Schools across the country have locked down dorms — and entire campuses — upon receiving threats or hearing reports of what sounded like gunshots. American University locked down its campus in Northwest Washington for nearly two hours one night in December after someone spotted a man with a gun, a man who turned out to be an off-duty police officer.

But what Georgetown faced was highly unusual. Ricin, a poison made from castor beans, is considered a weapon of terrorism.

On the scene at McCarthy by about 3:30 a.m., Gruber assessed the situation. A bag containing a suspicious powdery substance had been found in Room 615 and was secured. A student thought to be responsible for the threat, Daniel Milzman, was being questioned. A hazardous-materials squad from D.C. Fire and Emergency Medical Services tested the area and found no evidence that the substance had spread.

Gruber consulted with a D.C. battalion chief and decided to let dorm residents stay where they were — except for Milzman and his roommate in 615.

“There was really no need to evacuate anybody from the building,” Gruber said Thursday. “We didn’t consider it to be an ongoing threat in any way whatsoever.” The first notice that Georgetown sent to the campus community about the incident was an e-mail from Gruber at 9:38 a.m.

S. Daniel Carter, a campus safety advocate who works for a foundation started by families and relatives of victims of the 2007 Virginia Tech shootings, said Georgetown’s response seemed appropriate. Decisions about evacuations, lockdowns and emergency notification, Carter said, depend on whether a threat is contained.

“A gun is a simpler scenario,” Carter said. “A person with a gun moving about freely, that presents potentially a more clear threat than someone with a toxic substance who’s stationary.”

Milzman has been charged with possessing a deadly biological toxin in violation of federal law. Court documents indicate that Milzman made the ricin in his room and that prosecutors consider him a danger to the community. His attorney, Danny Onorato, said Tuesday at a detention hearing that Milzman was “a scared 19-year-old kid” and that the ricin “was not intended for anyone other than himself.”

For Georgetown, an 18,000-student university, the incident posed unusual challenges. This account draws on court documents and interviews with Gruber and Stacy Kerr, the university’s assistant vice president for communications.

At about 8:30 p.m. on March 17, Milzman texted a friend, who is a residential adviser, and asked to meet with him. At some point they met for about 90 minutes. Milzman, who was distraught, tossed a double-wrapped bag containing a gray powdery substance on the floor in front of the adviser and said it was ricin.

The adviser then contacted the university’s Counseling and Psychiatry Services Department. The call apparently happened after midnight.

The adviser then called the residential-living staff, which contacted university police at 1:58 a.m. An officer was dispatched to check the situation.

The incident went up the chain of command, following protocols. A police sergeant and captain were contacted. Gruber was called at home shortly before 3 a.m. Georgetown police called D.C. police at about that time. D.C. police and haz-mat teams responded. Senior university officials convened, some via teleconference, after 4 a.m. to monitor the situation. The FBI arrived at about 5:30 a.m.

Gruber, asked why the university did not evacuate the dorm or notify the community as soon as police received a report of potential ricin, said initial information suggested the threat was contained, which subsequent evidence confirmed.

“I heard on the phone it was sealed and wrapped in a package,” said Gruber, who has learned about ricin through classes on biological weapons. “I felt pretty good that it was sealed in a package. It wasn’t sitting on somebody’s desk, or in a cup, or something like that. If I had gotten information that it was discovered on a common-area table, or that the ricin had been dropped in a hallway, or somehow aerosolized, that certainly would have changed the direction I went.”

Before the incident, the university had ordered Milzman and another student to stay away from each other because of tensions between them. But Gruber said that information did not play a role in the initial response. “I didn’t learn about it until several hours later,” he said.

At 9:38 a.m., the university sent an e-mail from Gruber to the campus community and parents of students. Gruber said authorities had responded to a report of a hazardous substance at McCarthy Hall and that tests for “biological agents” were negative. Gruber said there was “no immediate risk” to the area and that students could remain in the dorm and all surrounding buildings.

At 11:01 a.m., the university sent an e-mail to about 20 students who live on the sixth floor of McCarthy, telling them to leave their rooms at 11:30 a.m. to aid the investigation. The university arranged for those students to stay in a hotel on March 18.

At 5:21 p.m. on March 19, Gruber e-mailed a final update that said the university “in an abundance of caution” had secured contractors to clean Room 615.

“There is no immediate threat to members of the Georgetown community,” Gruber said. The sixth floor went back to normal.

Experts said there is no script for the ideal response to particular campus incidents. The key, they said, is for universities to designate teams to assess situations as they arise. These teams must be vigilant and flexible.

“For the first 30 minutes, it might go from somebody doing a goofy prank to, ‘Oh, it’s real,’ ” said Andre Le Duc, who oversees emergency management for the University of Oregon and is active in the International Association of Emergency Managers. “When we’re assessing something, we know that things can go from zero to 60 [mph] in a heartbeat.”

Le Duc said universities must also be careful with the timing and content of announcements. “One of the things we have to balance is misinformation, disinformation can a lot of times be worse than the current situation.”