As they watched a Detroit Tigers baseball game, 40,000 sports fans were unaware that dozens of police, security guards and federal agents were swiftly searching the stadium for a possible bomb after someone phoned in a threat to 911.
Authorities made no announcement over the public address system. Ushers said nothing to the crowd.
Jason Miller, a suburban Detroit rabbi, left the game against the Los Angeles Angels on Tuesday night and didn't learn about the threat until the following day.
"I immediately started thinking, 'What if?'" he said. "What if they had to evacuate?"
Miller's concerns highlighted a vexing question for organizers of major public events: Should large crowds be informed about unconfirmed threats to their safety? Or is better to keep the matter quiet until investigators can check into it?
If authorities "evacuate every time there is a bomb threat, there will be a lot of empty places," said Steve Layne of Layne Consultants International, a Denver-based firm that specializes in the protection of libraries, museums and other cultural institutions and public facilities.
"You can't just pull a fire alarm and yell run. An evacuation in the middle of a ball game does cause some problems. You're running the risk of causing injuries."
The threat at Comerica Park was the third bomb threat to a Detroit landmark in less than a week. On Monday, someone claimed to have placed a bomb on the Ambassador Bridge linking Detroit with Windsor, Ontario, in Canada.
And on July 12, a similar threat forced the closing of the Detroit Windsor international tunnel beneath the river. In each case, emergency procedures went off without a hitch, and no bombs were found.
But Miller wasn't satisfied, saying fans "had a right to know what happened."
He said the park or the Tigers "could have in a very safe calm manner informed the crowd, if it was indeed a serious threat."
After the other threats, the tunnel and bridge were cleared of traffic while police and bomb-sniffing dogs searched for explosives.
In Detroit, police followed the stadium's security protocols, and a decision was made not to evacuate, said Donald Johnson, an inspector in the police department's Homeland Security unit.
"We don't make a decision to evacuate unless an actual device is found," Johnson said. "We don't panic. We go step by step. The thought was to find out what we actually had."
In a statement, the Tigers insisted the safety of fans, employees and players was the primary concern.
The team "worked closely and collaboratively with law enforcement officials and followed firmly established protocols," spokesman Ron Colangelo said.
The goal is not to create a panic, according to Lou Marciani, director of the National Center for Spectator Sports Safety at the University of Southern Mississippi at Hattiesburg.
"You don't want to get the spectators involved," he said. "Protocol is to do the search. Do it quickly, efficiently."
If the search had turned up a real bomb, an entirely different scenario would have unfolded, he said.
The National Center for Spectator Sports Safety is beginning to keep records of unclassified incidents at all stadiums worldwide. But no one knows how often stadiums receive bomb threats, Marciani said.
"Professional sports and many of the major colleges have evacuation plans," he said. "They do tabletop exercises and refine them all the time. There are pregame processes, in-game processes. If the protocol calls for the movement of people, it would have been done very efficiently in Detroit."
If a bomb is found "the decision to evacuate is made for you," Layne said. "Then you have to think about if there is staff available to assist moving crowds away from the device, if you have a safe assembly area."
It's not uncommon for sports stadiums — college and professional — to receive bomb threats, but few are evacuated, and the threats are rarely publicized for fear of inspiring copycats.
"You are not going to see it discussed unless it's a significant issue," Layne said.
A few thousand people were ushered out of Robert F. Kennedy Memorial Stadium in Washington, D.C., during a 2004 band competition after a bomb threat. A search of the stadium found nothing.
The announcement was made over the public address system.
Two years ago, some stands behind home plate and in front of the press box were cleared at the New York Mets' Citi Field after a suspicious bag was found under an empty seat during a rain delay.
No public announcement was made.
On Wednesday, authorities in Detroit were trying to determine if the Comerica Park threat was linked to the earlier threats at the bridge and tunnel. No one has been arrested.