"No one was found nor were there signs that a shooting had taken place in building, and there have been no reports of anyone injured," he said.
Bermudez declined to comment when asked if the call had been a hoax, saying only that the case was under investigation.
A few hours after the search began, the department's Twitter site said: "UAPD has cleared the Admin Bldg. No one was found, no injuries or signs of a shooting. The Stu Union IS OPEN."
A shooting at the University of Arizona's nursing school in October 2002 left three professors dead before the gunman killed himself.