Investigators began gathering evidence at the Yale Law School Thursday to determine more about the bomb that partially destroyed two rooms in the building Wednesday, State Police Lt. Col. Edward Lynch said at a press conference.

The building has been secured as an official crime scene, and Lynch said officials will likely have more information about the bombing in two or three days. On Thursday, FBI officials — who are questioning members of the Law School community — showed those interviewed a composite sketch of a person the FBI is trying to identify.

But officials said they currently have no suspects and do not yet know what type of device was used or where the bomb was planted. New Haven Mayor John DeStefano Jr. said there is no evidence the incident is linked to international terrorism.

University Secretary Linda Lorimer said at the press conference that the University’s Commencement activities will proceed as planned, but she said Yale will “step up” security for the event.

Lorimer said she hopes to finalize security plans for Commencement by midday tomorrow. She said the University is planning to implement many of the same protocols used when President George W. Bush ’68 spoke at Commencement in 2001.

“The actual details about how we are going to process people into Old Campus and into Woolsey Hall for Class Day and parking restrictions and the like, we will try to have a full recitation by Friday [at] noon, which we will post on the Web site” Lorimer said.

New Haven’s acting chief of police, Francisco Ortiz, said the NHPD will work with Yale Police and the Connecticut State

Police on security measures for Commencement, which will

likely include such procedures as checking bags.

“There’ll be extra security at all the entrances,” Ortiz said.

City spokesman Jim Foye said the New Haven Fire Department and the NHPD went through Southern Connecticut State University’s Lyman Auditorium with a bomb-sniffing dog in preparation for that school’s commencement on Thursday. They plan to do the same for University of New Haven graduation ceremonies Saturday, Foye said.

Lorimer said the University currently has “very well-developed security procedures and security controls.” But she said Yale may re-examine its policies.

Lorimer said Wednesday that the building where the bomb exploded was open all day, meaning anyone could have gained access to the space. Access to Law School classrooms is officially limited by a key card control system.

A student who works in a Yale laboratory said the head of facilities for the Engineering Department walked the halls of the facility today to ask employees if there was any dangerous material in the vicinity that could be stolen. The student said the man was asked by Yale security to perform the survey.

The explosion, which occurred at approximately 4:40 p.m. Wednesday, partially damaged Room 120 and the adjacent Alumni Reading Room on the first floor of the Law School building, but left no one injured. The blast also brought down a wall — made of wood and wallboard — between the two rooms.

DeStefano said there were strong indications that the incident was not linked to terrorism.

“There is nothing … that pulls it together, nothing leads us to that conclusion,” DeStefano said. “[That] doesn’t preclude it, but we don’t see it at this point.”

Lynch characterized the bombing as an “isolated incident.” DeStefano said there was no evidence to show the bombing was an “inside job.”

Lynch said the FBI has begun questioning those affiliated with the Law School, including all students, faculty and staff who were in the building at the time of the explosion.

“We’ve got all the names of everyobdy or anybody that was in the area that we’re aware of,” Lynch said.

But on Thursday, the FBI showed some of the people interviewed by the agency a composite sketch of a person authorities have not yet identified. Carsten Jungmann LAW ’03, who helped the FBI prepare the sketch, said he saw the man in Room 120 just two or three minutes prior to the explosion. Jungmann said the person was moving “awkwardly.”

Jungmann said he could not positively identify the person, but said he was white and clean-shaven, and had black hair that fell slightly below his ears.

Lynch said investigators have not yet gotten any new information from any of those questioned.

Lisa Bull, a spokeswoman for the FBI in New Haven, said the sketch has not yet been released to the public. She said the person is neither a suspect nor a person of interest, but someone investigators wish to identify.

“It could be a totally innocent person,” Bull said.

Timothy Schnabel LAW ’05, who was interviewed by the FBI, said in an e-mail that he was asked for his contact information, his location in the building at the time of the explosion, what he saw, whether he saw anything — or anyone — suspicious, and if he knew of anyone who might be angry at someone at the Law School.

All witnesses have cooperated with the FBI thus far, Lynch said.

Lynch would not confirm speculation that the device used was a pipe bomb.

Ortiz said it would be a “long, drawn-out investigation.” Lynch said investigators are now sifting through the debris and looking for trace forensic evidence.

“We’ve got guys on hand and knee, they’re sifting through debris,” Lynch said.

Foye said technicians are swabbing the floor for residue and are planning to fingerprint “every spot they could find in the building.” Representatives of New Haven and state police said they do not know how long the investigation will last or how long the building will be kept for investigation.

“The rubble itself is fairly extensive,” Lynch said. “[The investigation] is time-consuming.”

Lynch said there was some damage to the building’s windows. Some of the portraits that hung on the wall between the two rooms are still intact, officials said. The Associated Press reported that 300 rare books in a room underneath the reading room had been affected by water damage, but were not destroyed.

Lynch said the extent of the damage is not yet known because Yale representatives have not been able to assess the contents of the room for specific damage.

University officials said they were pleased with the work of the five agencies involved in the investigation — the FBI, the NHPD, the Connecticut State Police, the Yale Police and the federal Bureau of Alcohol, Tobacco and Firearms.

“We are enormously heartened by the teamwork of all of the law enforcement agencies,” Lorimer said.

Foye said the incident allowed the city to evaluate its first responders.

“[The fire and police departments] get an A+ grade [for yesterday],” he said.

Activity around the Law School and in New Haven has returned to normal, officials said, although the Law School building will remain closed through Friday. When they arrived on the scene Wednesday, law enforcement officials had cordoned off the entire block around the Law School.

“Frankly we’ve pretty much returned to normal, with the exception of the … Law School,” DeStefano said.

In a letter to the Law School community posted on school’s Web site, Yale Law School Dean Anthony Kronman said he was impressed with the resiliency of Law School students, faculty and staff.

“We have a mess to clean up,” Kronman wrote. “But we will repair all the damage that’s been done. And as we do, we will be grateful that no one was hurt and mindful of the hours we’ve spent in Room 120 and in the Alumni Reading Room, doing the things we’re accustomed to do freely and without fear in our beautiful building.”

DeStefano said the Law School building will remain closed through Friday, but could open again as early as this weekend. Students who live in the building were given temporary housing in Ezra Stiles College, University Secretary Linda Lorimer said. Law School exams, scheduled for this week, will now be administered in Sheffield-Sterling-Strathcona Hall, and deadlines have been extended.

It is not yet clear when students who left personal belongings in the building will be able to retrieve them, but some have been told that they may not have access to their belongings for five days.

The Law School administration has also made provisions for food service and has established a hotline for those in need of financial assistance.