Investigators searching for the killer who opened fire in a Brown University lecture hall have released new footage of a person they believe may be linked to the attack.

Four days after the gunman killed two people and injured nine others officials have still not identified a suspect, leaving the community on edge.

On Tuesday, police released “enhanced” footage of a person dressed in dark colours walking near the university two hours before the attack took place that was recorded by CCTV.

Officials are appealing for patience as the investigation proceeds, and have asked local residents to check security cameras to see if they have any footage of the suspicious “person of interest”.