The ongoing effort to find a man who walked onto Brown University ’s campus during a busy exam season and shot nearly a dozen students in a crowded lecture hall has raised questions about the school's security systems and the urgency of the investigation itself.

The shooter was still at large late Sunday, police said, adding they were releasing a man in his 20s who was briefly detained as a person of interest.

Law enforcement is pleading with the public to help in the manhunt, releasing additional images, requesting any new details or observations and offering a reward.

Providence’s Lippitt Park as temperatures hovered around freezing to honor victims of the mass shooting at Brown University. The shooting at the Ivy League school, which occurred as students took exams before winter break,