The Chechen men are believed to be the same ones pictured in images released by the FBI as suspects in the bombings that killed three people and wounded about 180.
The men are seen walking together near the finish line of the marathon.
The first suspect, killed by police, is seen wearing a dark hat, sunglasses and a backpack, CNN reported.
The second suspect, wearing a white cap, is the one who remains at large, police said.
The suspect hails from Chechnya or Turkey and has lived in the US for several years, Fox News reported citing a law enforcement source.
Authorities are investigating whether 19-year-old Dzhokhar A. Tsarnaev, of Cambridge, Massachusetts, and his brother may have had military training overseas.
Meanwhile, police said Indian-origin student Sunil Tripathi, a 22-year-old Brown University student, who went missing mysteriously March 16, was not a suspect in the Boston marathon bombings. Earlier, Tripathi was reported by some as the Boston bombing suspect number two.
Tripathi was first suggested as a suspect for the bombings on Reddit, then later by the Twitter account of Kami Mattioli, who knew the college student when he was in high school, the Inquisitr, a news website reported.
But the reports of Tripathi's involvement in the bombings turned out to be false after news media reported that the suspects were reportedly brothers from Chechnya.
On Friday, law officers swarmed through the suburb of Watertown, going door to door to track him down, CNN said citing Massachusetts State Police spokesman Col. Timothy Alben.
Police officers in full body armour, carrying automatic weapons, flooded the area.
Police ordered businesses to stay closed and told residents to stay inside and answer the door for no one but authorities.
The subway was shut down and every Boston area school, including Harvard University and Harvard Kennedy School, was closed.
Boston's public transit authority sent city buses to Watertown to evacuate residents while bomb experts combed the surroundings for possible explosives.
The violence began late Thursday with the robbery of a 7/11 convenience store, CNN said.
Soon after, in Cambridge, across the Charles River from Boston, a Massachusetts Institute of Technology (MIT) police officer was fatally shot while he sat in his car.
Police believe the bombing suspects were responsible for the shooting. The same two suspects, according to authorities, then hijacked a car at gunpoint in Cambridge.
They released the driver half an hour later at a gas station. As police picked up the chase, the car's occupants threw explosives out the windows and shot at officers.
Officers fired back, wounding one of the men, possibly the person identified by the FBI as suspect No.1.
The man died at Beth Israel Hospital. He had bullet wounds and injuries from an explosion, CNN said. The second man apparently escaped on foot.
Dzhokhar Tsarnaev, born in Kyrgyzstan, holds a Massachusetts driver's licence and lived in the suburb of Cambridge, NBC News reported citing law enforcement officials.
His brother, who was killed, was identified as 26-year-old Tamerlan Tsarnaev, born in Russia. He became a legal permanent resident in 2007, officials said.
Both men were believed to have military experience, and to have entered the country with their family in 2002 or 2003, when the family sought asylum, the channel said.
The nature of the military experience was not clear. Later, US Army officials told NBC that no one matching either name had served in the active-duty army, or the reserves.
The city of Cambridge awarded Dzhokhar Tsarnaev a USD 2,500 scholarship toward college in 2011, according to The Boston Globe.
A Maryland man who said he was the suspects' uncle told CNN affiliate WBZ that Tamerlan Tsarnaev "got what he deserved".
"What can I say for people who have been murdered? Sympathy," said Ruslan Tsarni, referring to those who died in the bombings at the Boston Marathon.
Meanwhile, Global Grind, another website focusing on celebrities, said Indian student Tripathi is not a suspect.
Although he was mentioned by the Boston police on their scanner as the person they were looking for, the site said it had learned that in fact Tripathi is not wanted by the police in connection with the marathon bombings.
But Tripathi still remains missing.
The search has been difficult and even involved the FBI. But despite pooling resources, the Inquisitr cited Providence Police Detective Mark Sacco as saying that they have no leads.
The former Brown student had been working through personal problems and was temporarily kicked out of Brown.
He left his apartment in the city without his cellphone, credit card, ID, and other personal effects. The effort to find Sunil Tripathi has involved social media, including his Twitter account, @findingsunny.
--IANS (Posted on 19-04-2013)