AP National Writer
BOSTON (AP) -- Moments after investigators went before television cameras to broadcast photos of 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.
Late Friday, the manhunt at last reached an end in the Boston suburb of Watertown, when police cornered 19-year-old suspect Dzhokhar Tsarnaev, hunkered down inside a blood-spattered boat parked in the backyard of a three-bedroom house.
The decision that led to their quarry -- whether or not to make photos of the suspects public -- was something of a gamble, one that investigators had to weigh carefully.
"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 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 brother, Dzhokhar, of time, anonymity and options.
By late Friday, many of the details in the chain of events that led to the older brother's death and the capture of the younger one after a massive manhunt were still unclear.
It began just after 5 p.m. Thursday, when investigators released the photographs and video of two unidentified suspects and asked for the public's help.
Just over five hours later, shots were heard on the campus of the Massachusetts Institute of Technology, across the Charles River from Boston in Cambridge. Ten minutes later, an MIT campus police officer who was responding was found shot multiple times in his vehicle and was later pronounced dead.
Soon after, two armed men carjacked a Mercedes SUV in Cambridge, holding the driver for about half an hour before releasing him unharmed. Police pursued and the men inside the vehicle threw explosive devices from the windows, while exchanging gunfire. A Massachusetts Bay Transportation Authority officer was wounded in the firefight and the older brother, Tamerlan Tsarnaev, was fatally injured and pronounced dead.
The hunt then continued for the younger brother, who fled on foot.
In the pre-dawn hours Friday, dozens of police officers and FBI agents converged on Watertown after gunshots and explosions were heard, ordering people to stay inside. But the search proved fruitless, leading authorities to shut down Boston's mass transit system and urge residents of several cities and towns to stay indoors.