Follow live updates as police seek to identify masked person as manhunt enters fourth day for Brown University shooting

Police in Providence, Rhode Island, on Tuesday released a new image of a person of interest in the deadly shooting at Brown University as the investigation entered the fourth day.

Experts told the Globe that every minute counts in an investigation like this, and that it is unusual to have so little information four days after a mass shooting.

Nuno Loureiro, a professor and director of MIT’s Plasma Science and Fusion Center, was found fatally shot at his Brookline home Monday night, officials said.

Questions swirl about campus security, the apparent lack of video evidence and whether the focus on the person of interest gave the attacker more time to escape.

Fifteen people - including a 10-year-old girl and a British-born rabbi - were killed when two gunmen targeted Jewish people attending a Hanukkah event.

Australia's federal police commissioner has confirmed that a mass shooting at Sydney’s Bondi Beach was a terrorist attack inspired by the Islamic State group.

Rhode Island Hospital officials said seven victims of the shooting remain at the hospital, where several are in critical condition.