Police are releasing a man detained in connection with the fatal shooting on the campus of Brown University in Providence, Rhode Island.
Two people were killed and nine others, all or nearly all of whom are also believed to be students, were injured in the attack on Saturday.
Earlier, three senior law enforcement officials briefed on the investigation told Sky's US partner NBC News the detained man, who is being released, was 24-year-old Benjamin Erickson, who had served several years in the US army.
The release means that the suspected gunman remains at large.
Providence mayor Brett Smiley said: "We know that this is likely to cause fresh anxiety for our community."
The shooting happened inside a classroom on the first floor of the Barus & Holley engineering building, a seven-storey structure home to much of the university's engineering and physics study and research.
Brown University provost Frank Doyle confirmed final exams were taking place in the engineering building when the gunman opened fire.
A police official told the AP news agency the gunman fired more than 40 9mm rounds. A gun has not been recovered, but officers did seize two loaded 30-round magazines.
A video released by officials shows a suspect walking down a street away from the campus and turning a corner, dressed in dark, loose-fitting clothing.
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