BOSTON (AP) - Moments after investigators went before television cameras to broadcast photos of the two men in ball caps wanted for the Boston Marathon bombing, queries from viewers started cascading in - 300,000 hits a minute that overwhelmed the FBI's website.
It marked a key turning point in a search that, for all the intensity of its first 72 hours, had failed to locate the suspects. While it's unclear how much the tips that resulted helped investigators zero in, experts say it instantly turned up already intense pressure on the two men to flee or almost certainly be recognized - increasing the chances they'd make mistakes that would lead to them being exposed.
The decision to ask the public for help also was something of a gamble, one that investigators had to weigh carefully.
This photo provided by Bob Leonard shows Dzhokhar Tsarnaev, left, and Tamerlan Tsarnaev approximately 10-20 minutes before the blast Monday at the Boston Marathon.
"It was a good decision to put this out to the public ... and this would have been a calculated risk. But the intent would have been to get these guys to change their pattern" of behavior, said Martin Reardon, who spent 21 years as an FBI agent and is now a vice president of security consultant The Soufan Group.
Releasing the photos greatly increased the odds the two men would be recognized and turned in, even as it significantly upped the chances they would try to vanish or commit more mayhem - exactly the scenario that has played out.
"Clearly these guys were reacting and responding exactly as (law enforcement) predicted," said Robert Taylor, a criminologist at the University of Texas at Dallas who studies terrorism. "If you saw your face on TV and everywhere else as associated with the bombing ... you would act irrationally, and that's exactly what they did."
After three days without being able to identify a suspect by name, investigators clearly made the decision to release the photos Thursday on the belief that, without doing so, the suspects might remain at large for weeks or months, with the chance to flee or to act again, said David Weinstein, a former federal prosecutor in Miami.
So with photos in hand, investigators made a choice deemed both necessary and prudent.
"And then the worst possible thing happens," Weinstein said. "They do actually begin their flight and then start to wreak vengeance on the whole city of Boston."
Weinstein, Reardon and other experts had differing opinions on whether investigators' decision to release the photos was worth the cost exacted by the two men: the killing of a Massachusetts Institute of Technology police officer, a carjacking, the shooting of another transit police officer and a block-by-block manhunt that led officials to shut down Boston and many of its surrounding suburbs.
But all agreed the photo release was pivotal in breaking open the case, because it instantly deprived suspected bombers Tamerlan Tsarnaev, 26, and his 19-year-old brother, Dzhokhar, of time, anonymity and options.
Investigators gathered hours of videotape footage from security cameras that scanned the area around the bombing and appealed to the public to turn in their own video and photos, for help in determining the sequence of events and identifying a suspect.
They then used software to search for certain types of objects or people matching a height and weight description. The software can also spot patterns that human analysts might not notice, such as a car that turns up in different places, said Gene Grindstaff, a scientist at Intergraph Corp., a company that makes video analysis software used by the FBI and other law enforcement agencies.
"Back in the days of 20 years ago, you were lucky if you had video and it was probably of poor quality and it took a tremendous amount of enhancement. Today you have a completely different issue," Grindstaff said.
By Thursday afternoon, the brothers had to know their options were narrowing quickly. And then the FBI released their photos around the world.
"I think this developed rather quickly last night," State Police Col. Timothy Alben said late Friday. "I would wager that most of the activity that was printed in the media yesterday forced them to make decisions or take actions that ultimately revealed who they were."