The twin blasts killed three and injured about 180 others Monday, sending shock waves nationwide. They left behind gruesome images of mayhem, destruction and shattered limbs.
President Barack Obama and first lady, Michelle, are scheduled to attend an interfaith service for the victims in Boston on Thursday morning.
And as the city prepares to pay tribute to the victims, details are trickling in about the tragic day.
In the images, one of the men is seen carrying a black backpack. An FBI official has said that the bombs were placed inside a black nylon backpack or bag.
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Authorities did not name the men, but their photographs have been distributed to law enforcement, the official said. The photos will not be released to the public for fear of impeding the investigation, according to the official.
Earlier Wednesday, two sources with knowledge of the investigation identified a man as a possible suspect in the attack, but did not name him.
Seen on a video, the man wore a white baseball cap. One of the sources added that the cap was on backward and the man was also wearing a light-colored hooded sweatshirt and a black jacket.
It was not immediately clear if he is one of those alluded to in the photographs distributed to law enforcement officials.
Investigators are closer to cracking the case “every hour,” Massachusetts Gov. Deval Patrick said. He urged patience to allow authorities space to do their job.
“I wish they had nailed the perpetrator within minutes of this catastrophe, but I understand from experience it’s going to take some time,” he said.
‘Make room for love’
Four days after the bombing, emotions are still raw.
But those who lived through the blasts — and those touched by the tragedy — are slowly picking up the pieces and trying to move on.
But as the initial shock subsides, some are determined to move past the grisly attacks.
It’s time to “make room for love, said Lisa Conti, a graduate student in Boston. “Imagine how much deeper the wound would be if we filled the empty spaces with hate instead of love.”
In Michigan, Hamilton Elementary School students created a “finish line” by standing on either side of the hallway so their principal could finish the marathon interrupted by the cruel blasts.
“We felt bad that she couldn’t finish the 26.2 miles. So, we decided that we would help her finish,” fourth-grader Ryan Smalley told CNN affiliate WDIV.
The students cheered for Principal Pam Mathers as she dashed to the finish line, high-fiving the students along the way. Some teachers watched, tearfully.
“You know what? I may not have gotten the medal but I’ve gotten many many more rewards from you,” Mathers said Wednesday. “All of you are my medals.”
But for Candace Rispoli, who witnessed the bombing, the pain was still too raw.
“My hands have still not stopped shaking,” Rispoli said.
Details of bombs
Investigators say the bombs, which exploded 12 seconds apart, were designed to deliver the most vicious suffering.
One was housed in a pressure cooker hidden inside a backpack, the FBI said. The device also had fragments that may have included nails, BBs and ball bearings, the agency said.
The second bomb was in a metal container, but it was unclear whether it was in a pressure cooker as well, the FBI said.
Photos obtained by CNN show the remains of a pressure cooker found at the scene, along with a shredded black backpack and what appear to be metal pellets or ball bearings.
They were sent to the FBI’s national laboratory in Virginia, where technicians will try to reconstruct the devices.
In the past, the U.S. government has warned federal agencies that terrorists could turn pressure cookers into bombs by packing them with explosives and shrapnel, and detonating them with blasting caps.
While the clues moved the investigation forward, it is still unclear whether the attack was an act of domestic or foreign terrorism.
Authorities sifted through thousands of pieces of evidence and a mass of digital photos and video clips. They have pleaded for the public’s help in providing additional leads and images.
The blasts left three people dead.
Martin Richard, an 8-year-old boy with a gap-tooth grin and bright eyes. He loved to run and play in his yard.
Krystle Campbell, a 29-year-old freckle-faced woman described by her mother as having “a heart of gold.”
The third victim was Lingzu Lu, a graduate student at Boston University who had moved to the city last fall, making friends and soaking up new experiences.
Of the approximately 180 people injured, 66 remain in area hospitals, according to the latest CNN tally.
Dr. George Velmahos, head of trauma care at Massachusetts General Hospital, said his team found “numerous” metal pellets and nails inside patients’ bodies.
“There are people who have 10, 20, 30, 40 of them in their body, or more,” Velmahos said.
Dr. Ron Walls also said one patient had more than 12 carpenter-type nails.
“There is no question some of these objects were implanted in the device for the purpose of being exploded forward,” he said.