The suspected suicide bombing at an Ariana Grande concert in the British city of Manchester killed at least 19 people and injured dozens. It is raising new questions about how authorities can better protect large venues.

The bombing happened near an entrance to the 21,000-seat Manchester Arena just minutes after Grande’s concert ended.

Michael Downing, executive vice president of security for Prevent Advisors, which specializes in arena and stadium security, told the Los Angeles Times that many American and European venues already use metal detectors, bomb detection technology and armies of security guards and cameras inside the facilities.

But the Manchester attack reveals the need for more vigilance in areas outside those security zones, such as transportation centers, walkways and parking lots, said Downing, the former head of counter-terrorism for the Los Angeles Police Department.