The New York Police Department is searching for several people who were spotted with suspected assault rifles in Staten Island on 17 July.
A retired NYPD officer took photos of the group, which are now being examined by police.
Law enforcement sources said the group may have been carrying paintball guns.
The NYPD has issued a "be on the lookout" alert following the potential security threat, and is searching for two SUVs with the plate numbers A83FCB and PSJ52V.
The photos, taken in the Midland Beach parking lot, show unknown individuals transferring the alleged weapons between two vehicles with New Jersey license plates.
Police have been on high alert following the fatal shooting of four US marines in Tennessee on 16 July.