The crowded scene in central Boston during Monday’s marathon was recorded by surveillance cameras and various media outlets there to cover one of the biggest events in the city’s sporting calendar.
That footage provided investigators with significant video of the area before and after the two blasts.
After combing through this footage investigators believe they have spotted a suspect and have a clear image of him, though sources said he had not yet been identified.
CNN carried reports that this individual was wearing a white baseball cap.
It said the man had the hat on backwards and was wearing a light-coloured hooded sweatshirt and a black jacket. Key footage is believed to have been taken from the Lord & Taylor department store which was very close to one of the bomb sites.
Yesterday evening, reports spread rapidly around the world that a suspect had been taken into custody.
Boston Police and the FBI were forced to issue statements refuting the claims.
The FBI statement said: “Contrary to widespread reporting, there have been no arrests made in connection with the Boston Marathon attack.
“Over the past day-and-a-half, there have been a number of press reports based on information from unofficial sources that has been inaccurate.
“Since these stories often have unintended consequences, we ask the media, particularly at this early stage of the investigation, to exercise caution and attempt to verify information through appropriate official channels before reporting,” it read.
Shortly after the false arrest report, hundreds of people as well as dozens of media organisations flocked to Boston’s federal courthouse believing there had been a breakthrough in the investigation.
Amid reports of a bomb threat, officials ordered staff, media and attorneys to evacuate and move at least 100 metres away.
Bomb-sniffing dogs and fire engines arrived at the courthouse but no device was found. A police press conference which was expected to give an update on the investigation was postponed late last night.
Meanwhile, officials at three Boston hospitals that treated the most seriously injured said they expect all of patients to survive.
The trauma surgery chief at Boston Medical Center said a five-year-old boy was among the 19 patients still being treated there for injuries received during the marathon bombings.
Dr Peter Burke said the hospital treated 23 people following the blasts. He said two patients, including the five-year-old, remain critical, but that all patients are making progress.
“We have a lot of lower extremity injuries, so I think the damage was low to the ground and wasn’t up,” he said.
“The patients who do have head injuries were blown into things or were hit by fragments that went up.”
Earlier in the day it emerged two letters with traces of poison had been sent to US President Barack Obama and a US senator with the FBI confirming that both were related.
The two letters were postmarked from Memphis, Tennessee and dated April 8. They each contained a note which read: “To see a wrong and not expose it, is to become a silent partner to its continuance.”
Both were signed: “I am KC and I approve this message.”
The FBI said that the substance in the letters had preliminarily tested positive for ricin.
The letters to senator Roger Wicker, a Republican, and to Mr Obama were intercepted at off-site mail depots.
Police also searched the US Capitol complex amid a flurry of reports of suspicious packages and envelopes.
Reports of suspicious letters also came in from congressional offices in Michigan and Arizona as police investigated the discovery of at least three questionable packages in Senate office buildings.
The FBI said there was no indication of a connection between the letters and the bombing at the Boston marathon.