(TNS) -- UNC officials are looking into what Chancellor Carol Folt termed a “completely unacceptable” failure of the system they use to warn students, faculty and staff of on-campus safety threats.

The review follows a pair of armed robberies that happened on campus at about 11 p.m. Wednesday. Campus police are looking for two men who were in a white, four-door sedan and used handguns to threaten their victims.

Authorities implemented part of the alert system late Wednesday night, sounding sirens that by definition mean there’s an emergency somewhere on campus that requires people to go inside or take cover immediately.

The problem is that they’re also supposed to back up the sirens with Web bulletins, email, text messages or social media postings that explain what’s going on.

On Wednesday, those messages were 45 minutes late in trickling out.

“The system failed,” officials said in a succinct follow-up advisory on the “Alert Carolina” Web site.

Folt told campus trustees much the same thing on Thursday, saying the incident wasn’t “a high moment” for the university’s communications effort.

In a later interview she also made it clear she has a zero-defects attitude on the point.

“Even if we’re successful 99 times out of 100, that extra one is really important,” she said, adding that she expects “a full accounting immediately” and that the review was already underway.

Officials gave the campus population the all-clear near midnight on Wednesday.

The Web bulletin advising of the emergency was time-stamped 11:35 p.m. Wednesday. A related Facebook posting warning of “an armed and dangerous person on campus” appears to have gone up around midnight.

Commenters on the Facebook posting indicated that email and text-message advisories were likewise slow. One said the Alert Carolina system has been “next to worthless for the last five years.”

Folt and other officials stressed that the customary building-lockdown procedures had taken effect immediately, everything but the notification system working as planned.

The robberies themselves remain under investigation.

The first of them happened near Aycock Hall and Raleigh Road. Two men accosted a third who was walking near the residence hall, which is on the eastern part of campus.

The two flashed a handgun and ordered the victim to hand over his wallet.

The second robbery happened moments later. A woman reported being approached by the same two men, now in the white car, who pulled a gun and asked for property.

Campus police said the men they’re looking for in connection with the incident are black and in their early 20s. One was about 5 feet 10 inches tall and stocky, with a dark complexion, round face, “a short fade haircut” and had been wearing a dark tank top.

The other was about 6 feet tall with a thin build, dark complexion and short hair. He wore a white t-shirt and long khaki pants.

Police urge anyone with information that might help the case to call 911.

©2015 The Herald-Sun (Durham, N.C.) Distributed by Tribune Content Agency, LLC.