Two elite Northeast institutions of higher education have been rocked by horrific acts of gun violence, just days apart.

In the first incident, two people were killed and nine were injured in a mass shooting at Brown University, when a gunman opened fire on the Rhode Island campus, officials said. A person of interest seen in the area before the shooting is being sought, authorities said.

Two days later, some 50 miles away in neighboring Massachusetts, an esteemed professor at the Massachusetts Institute of Technology was killed in a shooting at his home, officials said.

No arrests have been made or alleged motives announced in either case. Though the two shocking incidents may be linked, multiple sources briefed on the investigation tell ABC News.

Here’s how the tragic shootings unfolded.

Dec. 13

A person of interest sought in the Brown shooting is seen in surveillance footage walking through a residential neighborhood near the Providence campus, beginning around 2 p.m., in images and footage released by the FBI. But police have said they believe he had been around the Brown campus as early as 10 a.m. that day “casing out the area.” The individual is seen dressed from head to toe in dark clothing, including wearing a surgical mask over his face.

The shooting at Brown occurrs at 4:03 p.m. in a lecture hall in the school’s Barus & Holley Engineering building during a final exam review, according to authorities and school officials.

Just after the shooting, a security video captures the person of interest emerging onto Hope Street from what investigators described as “lot 42” on the Brown campus.

The last video in the FBI’s timeline shows the individual walking north on Hope Street at 4:07 p.m.

Dec. 14

A man initially thought to be a person of interest in the Brown shooting is detained at about 3:45 a.m. at a Hampton Inn in Coventry, Providence, according to law enforcement sources and police, though that individual is released hours later without being charged.

Rhode Island Attorney General Peter Neronha says during a late-night press conference that there had been evidence pointing to this individual, but that evidence “now points in a different direction.”

Dec. 15

Authorities release new images and video of the person of interest in the mass shooting at Brown and the FBI announces it is offering a reward of up to $50,000 for information leading to the identification, arrest and conviction of the individual responsible.

That night, authorities respond to a residence in Brookline, Massachusetts, after receiving a report of a man shot at his home, according to the Norfolk County District Attorney’s Office.

The victim is identified by the office as 47-year-old Nuno Loureiro, a Portugal native who is a faculty member in MIT’s departments of Nuclear Science & Engineering and Physics and the director of MIT’s Plasma Science and Fusion Center.

Dec. 16

Loureiro is pronounced dead at an area hospital in the morning, according to the Norfolk District Attorney’s Office.

Authorities release a new image and enhanced video of the person of interest sought in the Brown shooting.

Dec. 17

Providence police announce they are seeking the public’s help in identifying and speaking to an individual “who was in proximity of the person of interest” in the Brown shooting. Police release images of the unknown individual.

Dec. 18

The mass shooting at Brown and the deadly shooting of Loureiro may be linked, multiple sources briefed on the investigation tell ABC News.

The information about a possible connection between the two incidents was developed in the last 24 hours as detectives working on both cases compared notes, the sources say.

Law enforcement officials identify a possible suspect in connection with the Brown shooting and issue a warrant for the individual’s arrest, multiple sources tell ABC News.

ABC News’ Josh Margolin, Aaron Katersky and Bill Hutchinson contributed to this report.