(AP) - Bob Leonard and his family were Boston Marathon veterans and he preferred a spot not too far from the finish line to photograph runners as they concluded their 26.2-mile run. The area was less congested and over the years he learned that the men and women in the lead there usually went on to win.
With his Nikon, Leonard snapped about 10 to 20 photos a minute Monday, capturing group after group of finishing runners and the crowds lining the route.
Three days later, when the FBI released images of the suspects in the Boston Marathon bombing, Leonard used the time stamp shown on them to narrow his search of the hundreds of photos he had taken that day. He realized that he, too, had photos of the faces of the two men authorities were searching for.
He uploaded them to the FBI and Friday morning, he saw his cropped photos all over the morning news.
"That finally gave them a good facial picture," the 58-year-old electrical engineer said. "It was a pretty good breakthrough."
The two men were later identified as brothers, 26-year-old Tamerlan Tsarnaev, who was killed in shootout with police overnight Friday, and 19-year-old Dzhokhar Tsarnaev, distinctive in his backward white baseball cap. The younger man was captured Friday night after a daylong siege of a Boston suburb.
"They actually stood in that corner for quite a bit of time," Leonard of Taunton, Mass., said of the men, just before the younger brother was caught.
After combing the digital images, he was sure he had something the FBI could use. He tried to upload them to an FBI site that it had asked the public to use. Then he called the hotline number and was on hold for about 40 minutes, the response was so overwhelming. He finally got an FBI spokesman, who told him to upload them to another site. Within 20 minutes, someone from the Department of Homeland Security called him back.
"They were on the news ... clear pictures of the two subjects and those were the pictures that I sent in," said Leonard, who started photography as a hobby when his sons played high school sports.
He was not the only picture-taker to help with images of the suspects. Seconds after the bombs exploded, David Green pulled out his smartphone and took a photo of the chaos developing a couple hundred yards in front of him _ the smoke, the people running in panic.
The Jacksonville businessman then put his phone back in his pocket and went to help the injured. It wasn't until Thursday, when officials released surveillance video of the two suspects, that Green realized what he had _ a picture of Dzhokhar Tsarnaev walking away from the scene.
When Green's photo of one of the Boston bombing suspects fleeing the scene first surfaced, there was considerable doubt as to its authenticity because of the very low resolution of the image, which made the photo appear to be a composite image. When Green later provided the high-resolution frame directly from his cellphone, editors of The Associated Press were able to establish its authenticity based on the improved resolution as well as the time the photo was taken. The AP has established an exclusive arrangement for distribution of the photograph.
Green, back at his home in Florida, wore his yellow and blue Boston Marathon jersey as he talked about the now-famous photo, his finisher's medal from the race propped on a shelf in his home office.
Green, 49, had finished Monday's marathon in 3 hours and 17 minutes, about an hour before the blasts.
After he recovered, he went back to Boylston Street, where the finish line is located, to watch the rest of the race with his friends. He realized his phone was dying, so he went into a nearby store with a recharging station.
About 15 minutes later, he was walking back to his friends when the first bomb went off.
"I thought maybe it was a cannon," Green said. Then the second one exploded as he was walking toward it.
"When I saw it, I pulled out the camera and immediately took that picture," Green said.
He then put it back in his pocket and went to help the injured, including a boy and others who were missing limbs.
"It was like battle _ a lot of noise, a lot of smoke, people coming at me in a panic," he said.
A short time later, his friend Jason Lubin texted him and asked if he was OK. He replied with the photograph and a note: "It was just in front of me."
Lubin said Thursday, after the FBI released photos of the two suspects, that he decided to take a closer look at Green's photograph _ on the off chance Green had captured anything unusual. He pulled up the photo on his smartphone and zoomed in on the crowd. There in the lower left corner was Dzhokhar Tsarnaev walking around a corner, his backward white baseball cap standing out amid the dozens of panicked people fleeing.
"I literally had to sit down," Lubin said.
Green contacted the FBI, which told him to send them a copy of the photograph.
"He is calmly walking, without panic," Green said of Dzhokhar Tsarnaev.
Leonard also took pictures of the chaotic aftermath, smoke five stories high from the explosions that he said were deafening. He also saw a person who lost a limb before police rushed everyone away from the scene.
"The sense of loss tears your heart apart when you hear the victims' stories," said Leonard, who has lived in Taunton, about 30 miles south of Boston, since 1986 and knows what the race means. "It's just so senseless."
Associated Press writer Russ Bynum in Jacksonville Beach, Fla., contributed to this report.
(Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)