Authorities intensified their search Monday for the gunman who killed two students and wounded nine others in a shooting at Brown University, as concerns grew over campus security and how the attacker managed to flee.

Police and federal agents went door to door in nearby neighborhoods, checking yards and asking residents for surveillance footage that could help identify the suspect. Investigators released new videos showing a masked man in a dark, two-tone jacket before and after Saturday’s attack, but his face remains obscured. The FBI described the suspect as about 5 feet 8 inches tall with a stocky build and announced a $50,000 reward for information leading to an arrest and conviction.

The search gained urgency after police acknowledged they had released a person of interest on Sunday, saying evidence no longer supported his involvement. The reversal raised public frustration and questions about whether the shift allowed the real suspect more time to escape.

The shooting occurred in an auditorium-style classroom where students were studying for finals. Among those killed was Ella Cook, a 19-year-old sophomore active in campus politics and church life, and MukhammadAziz Umurzokov, an 18-year-old freshman who had overcome significant childhood health challenges after immigrating from Uzbekistan.

As of Sunday, only one of the wounded had been released from the hospital. Several others remained in critical but stable condition, including students from outside Rhode Island.

Brown lifted its lockdown, but unease lingered among students, parents and prospective applicants. Some nearby universities and Ivy League schools announced heightened security, particularly around religious events.

Investigators said they are still working to trace the suspect’s movements and determine how he entered the classroom, noting limited camera coverage in the area. The attack, which unfolded during finals week, triggered hours of chaos on campus and renewed debate about safety at open university campuses.