Reports of shots fired on Northwestern University's Evanston campus; no active shooter

CHICAGO (CBS)-- Shots were fired on Northwestern's Evanston campus Sunday night. 

School officials alerted students about an active threat just before 11 p.m. The shots were reported near the school's music building at 70 Arts Circle Drive.

The initial alert at 10:53 p.m. stated, "There is an Active Threat event on the Evanston Campus. Run, Hide, Fight. Take proper shelter. Lock and/or barricade doors. Await further information." 

Police confirmed Monday, there was not an active shooter. Northwestern University police found bullet casings in the area but did not find anyone injured.   

Students were told to shelter in place until an all-clear was issued within an hour of the first alert. 

No suspects are in custody. 

This is a developing story.