Authorities are still searching for who was responsible for the deadly terrorist attack which killed three people and injured 183 at the Boston Marathon, as they say the investigation is 'still in its infancy.'
Speaking Tuesday afternoon at a press conference, the FBI agent in charge, Rick DesLauriers, said they have received more than 2,000 tips which they have looked into but the range of suspects still remains wide open.
He said authorities are working around the clock and forensic evidence has been sent to FBI labs in Virginia to be analyzed and reconstructed.
Scroll down for videos
Forensics: Investigators surveyed the site of a bomb blast on Boylston Street the day after two explosions hit the Boston Marathon
Investigators in haz-mat suits are seen examining the scene of the second bombing as they try to piece together fragments of the bomb
He also asked people to report anyone who talked about targeting Monday's race or showed interest in explosives or if anyone was seen carrying a heavy nylon bag in the area at the time.
'Someone knows who did this,' DesLauriers said. 'Co-operation from the community will play a crucial role in this investigation.'
No one has claimed responsibility for the attack and authorities do not even know if it was a group or an individual, Al Qaeda or a sympathizer, a lone wolf or a right-wing extremist group capitalizing on it being Patriot's Day.
A Saudi student was detained for 'acting suspiciously' at the marathon finish line yesterday but was later ruled out as a suspect by federal officials after they raided his apartment.
Officials said they were talking to Abdulrahman Ali Alharbi only as a witness.
The 22-year-old, who is studying English, is still in hospital after suffering from serious burns and is said to be cooperating fully with authorities. He was tackled to the ground by a civilian who believed he was acting suspiciously.
It was also revealed Tuesday that important clues are being collected from the victims themselves.
Doctors at Tufts Medical Center said they had removed countless pieces of shrapnel from injured bodies and were turning them over to police and federal agents.
Dozens of pellets and nails were collected and sent away as evidence. Some had as many as 40 fragments in their body.
FBI release images of bomb used at Boston Marathon
Detectives and bomb disposal officers raided Abdulrahman Ali Alharbi's apartment Monday night in the Revere area of Boston but he was not charged with anything
'Crude bombs': Both of the bombs were small, likely homemade devices and initial tests showed no C-4 or other high-grade explosive material
Police and federal officials exit an apartment complex at 364 Ocean Avenue with a possible connection to the earlier explosions that occurred during the Boston Marathon on Monday
WAS THE TIMING SIGNIFICANT? PATRIOTS' DAY IS REVERED BY RIGHT-WING GROUPS OPPOSED TO THE FEDERAL GOVERNMENT
Yesterday's attack took place on Patriots' Day, which marks the first battle of the Revolutionary War and the 'shot heard 'round the world.' It is a day held in reverence by right-wing domestic groups and others who oppose the federal government.
The 1995 bombing of the Oklahoma City federal building, which killed 168, occurred the day after Patriots' Day. Bomber Timothy McVeigh was said believe the date was significant.
The federal siege of the Branch Dravidian compound, which left 82 members of the cult dead, began on Patriots' Day in 1993.
Today is also Tax Day, when federal income tax returns are due. In recent years, it has been seized on by members of the Tea Party as cause to protest federal government policies and tax rates.
A Justice Department source tells MailOnline that authorities are looking into the possibility that the Boston attack, which killed three and injured 144 more at the finish line of the Boston Marathon, could have been planned to coincide with Patriots' Day.
President Barack Obama himself acknowledged the significance of the holiday during his briefing this afternoon.
'Today is Patriots Day,' he said. 'A day that reflects the freedom Boston has celebrated throughout its history.'
Meanwhile, a Boston University graduate has been revealed as the third victim but his or her name has not yet been released.
The Department of Homeland Security secretary today added there is no indication the bombs are part of a wider plot as the laborious process of interviewing the thousands of witnesses gets underway.
The two bombs that were used were made from six-liter pressure cookers crammed with shards of metal, nails and ball bearings and stashed in black backpacks.
The cruelly-designed bombs have 'frequently' been used in Afghanistan, India, Nepal and Pakistan, according to a 2010 Homeland Security Department pamphlet - hinting at the origins of the bombers behind the worst terrorist atrocity in the U.S. since 9/11.
The FBI is currently putting together the hundreds of hours of video footage both from private and public surveillance and those individuals attending the race.
They will examine the faces of everyone who was in the area at the time and use facial recognition matching software, drawing on drivers license, passport, and visa databases.
Phone records will also be scrutinized and investigators will look through right wing chat rooms and forums to see if there is any mention about the bombs or who is responsible.
The U.S. government has warned federal agencies in the past that pressure cookers have been used in various parts of the world to make bombs.
A Department of Homeland Security memo called it 'a technique commonly taught in Afghan terrorist training camps'.
Kitchen bomb: The pressure cooker bomb is known as a 'highly effective' weapon of al Qaeda
Aftermath: Smoke billows over the finish line after the first bomb was detonated, inflicting tragedy and panic at the race'Typically, these bombs are made by placing TNT or other explosives in a pressure cooker and attaching a blasting cap at the top of the pressure cooker,' the memo said.
Terrorism expert Jeffrey Beatty spoke to CNN and said they are often used by Taliban and al Qaeda militants to make IED's but stressed: 'That doesn't mean it was the Taliban -- other people can read about this.'
Tuesday, President Obama once again addressed the nation about the bombs and confirmed it was an 'act of terror.'
He admitted they did not know who was behind it or why, if it was an international or domestic organization, or perhaps a 'malevolent individual.'
He lauded the response of the runners, spectators and first responders in the wake of the attack.
'If you want to know who we are, what America is, how we respond to evil, that is it: selflessly, compassionately, unafraid,' he said.
Obama said investigators 'don’t have a sense of motivation yet' as they begin to evaluate the attack but despite the atrocity of it, he declared: 'The American people refuse to be terrorized.'
Richard DesLauriers, the special agent in charge of the FBI's Boston Division, said: 'We will go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime -- and we will do everything we can to bring them to justice.
'Our mission is clear: to bring to justice those responsible...The American public wants answers. The citizens of the city of Boston and the Commonwealth of Massachusetts want and deserve answers.'
He said investigators had received 'voluminous tips' and were interviewing witnesses and analyzing the crime scene.