Updated 3/16/19, 11:07 p.m.:
The University of Michigan's Public Affairs office released a statement late Saturday evening regarding the day's earlier emergency alert. In it, they noted the spread of misinformation "outside of DPSS channels" contributing to the confusion about what was happening on the Ann Arbor campus.
DPSS issued updates on the emergency alert while the search process continued, but there is no question that incorrect information was being shared throughout the community outside of DPSS channels. It is important to closely follow DPSS on these matters and to make sure you are signed up for the U-M emergency alerts.
They also confirmed reports of popping balloons being the initial cause for concern:
Officers were able to confirm a report of balloon popping activity in the area where the sounds of shots fired were reported to have been heard. Preliminary information indicates that the activity was not the result of malicious intent.
An emergency alert was issued by the University of Michigan Saturday afternoon warning of an active shooter on its Ann Arbor campus. University police confirmed there was no active threat approximately an hour later.
Initial alerts were emailed, texted, and issued on social media at 5:04 p.m. reading, "Active shooter in Mason Hall. Run, hide, fight."
20 minutes later, the warnings were changed to an "unconfirmed shooter," before the UM Division of Public Safety and Security issued a statement saying, "There does not appear to be an active threat to the community."
UM EAlert Ann Arbor UPDATE - There continues to be no indication of an active threat to the community. Police continue to investigate. Please stay away from Angell and Mason Halls.
— U-M DPSS (@umichdpss) March 16, 2019
The area around Mason Hall, including libraries and classrooms, were being cleared by police. An "all clear" was given at 7:50 p.m.
The timing of the first reports came at 4:35 p.m., around the same time and place a vigil for the victims of Thursday's mass shooting in New Zealand was being held.