The school, which is based in Washington, DC, initially stated on Twitter that law enforcement officials were focusing their investigation on the "Main Campus, East Campus, and 3201 New Mexico." At the time, shuttle operations had been suspended for the duration of the search as students and staff members were urged to "shelter in place."
According to local media reports, the lockdown was being done as a "precautionary measure" after local police received a call about a person near the campus "with a gun on their hip."
Officials with the Metropolitan Police Department of the District of Columbia, American University Police Department and the US Secret Service were involved in the investigation.
Images of the campus surfaced on social media throughout the investigation.
The university first indicated in a tweet that students and staff on campus had not received lockdown alerts due to a "technical issue," a mishap that has since been resolved.