Centennial Olympic Park has been the surprise hit of the Summer Games, a relaxed oasis of free movement in a city where sports venues had been transformed into fortresses.
On Saturday, however, the downtown park was closed indefinitely as investigators examined the debris scattered across it by an early morning pipe bomb that killed one person and injured more than 100.
And Olympic security planners were left to face a stark reality:
Whoever planted the bomb struck unerringly at one of the weakest points in the massive, $300-million security operation.
"Obviously, when something like this happens, you want to re-evaluate where you are," said Woody Johnson, the FBI agent in charge of the case. "We'll . . . look at whether we need increased security at the park when it reopens."
In this case, the warning from the 911 call may not have been passed through the various layers of communication in a speedy manner.
During the next 18 minutes, hundreds of people milled about the area where the bomb was located.
Johnson said the FBI will evaluate whether officials moved fast enough. If that is the determination, then part of the reason could be the complex system responsible for coordinating the dozens of federal, state and local security agencies.
"It's not your typical Atlanta day when you call the Atlanta P.D. and they arrive in three minutes and take the bomb," said a federal law enforcement official.
Another problem: The thrust of security has been concentrated on the venues and the Olympic Village. There were signs of increased policing at those areas Saturday. Heavily armed soldiers were evident and ticket-holders were greeted by lengthier security checks.
But because the park was designed so people could come without the tickets and credentials needed for Olympic events, perhaps no place was more vulnerable.
The 21-acre site was thronged, day and night, with people strolling, listening to concerts, buying souvenirs, swapping Olympic pins and just hanging out.
Although it was patrolled by a large number of police officers, many people carried in unchecked bags. Revelers said the only thing guards appeared interested in was people carrying alcoholic drinks.
Mayer Nudell, a Washington-based anti-terrorism consultant, said it stood out in a sea of highly secured venues.
"It was a calculated risk I doubt will ever happen again at an Olympics," he said.
Brent Brown, who heads a security firm in Atlanta, said he took his family to the park on Friday.
"It is like a big fair, with many entrances and exits," said Brown. "That surprised me. I did expect to have to go through some perimeter screening."
Asked if he thought security should have been tighter at the park, Billy Payne, president of the Atlanta Organizing Committee, said: "I probably would have interpreted that in the context of "Can you perfectly secure all public places.' The answer, obviously is not."
Security forces and measures
The Atlanta Olympics is guarded by one of the largest and most complex peacetime security operations ever mounted in the United States _ at a cost that could exceed $300-million. However, security at the site of Saturday's bomb blast, Centennial Olympic Park, was minimal; officials said they did not want to limit access to the park and all the free activities there. Here's a look at the security measures in effect in other areas:
Here is a breakdown of the approximately 30,000 Olympic security personnel in Atlanta and other parts of Georgia:
14,000 U.S. Army troops, assigned such tasks as checking cars entering parking garages as well as non-military duties such as driving buses and watering lawns.
10,000 private security guards, staffing security check points for the main media center, sports venues and other Olympic sites.
4,500 public safety personnel with the State of Georgia Olympic Law Enforcement Command, assinged to protect state-owned venues under SOLEC's direction.
1,500 Atlanta Police Department members.
1,100 foreign law enforcement volunteers assinged to help guard sports venues in central Atlanta.
Among the other security steps being used around the Atlanta area:
Soldiers are using illuminated mirrors to check under cars parking downtown. Saturday, soldiers crawled under vehicles moving into the secured area to get closer looks.
A 10-foot, touch-sensitive fence around the Olympic Village is linked to remote control cameras.
Large numbers of surveillance cameras, some of them concealed.
Water venues equipped with sonar devices to detect potential underwater threats.
40 bomb-sniffing dogs on standby around the Olympic complex.
Downtown manhole covers have been welded shut.
Along with the heavy presence of security personnel, organizers are also using sophisticated security devices. Among them:
Spectators will have to carry their tickets with them at all times. Everyone else, including the athletes, must wear badges that have their name, photo and a bar code. Hand-held scanners are used to read the encrypted information.
At some security checkpoints, scanners will read the handprint of athletes, coaches and officials before allowing them to pass. Here's how it works:
Athlete wears I.D. badge with microchip that stores data & handprint.
Athlete places hand in scanner which creates a 3-D image of hand, measuring features such as knuckle height and finger width.
When the scanned image matches the microchip image, clearance is granted.
Sky Watch security
Sky Watch, a crime prevention and surveillance system, will be used to provide additional security during the Olympics.
Sky Watch cab:
Allows one officer to monitor area previously covered by three or more officers.
Elevates security officer from ground to 20 feet in seconds.
35 Sky Watch units will be used during the Olympics.
The blimp watch
A giant blimp hovers overhead, transmitting video surveillance images to a command center on the ground.
Sources: Associated Press, Knight-Ridder Tribune, Reuters