Officials take crime scene photos two days after two explosions hit the Boston Marathon in Boston, Massachusetts, yesterday. Photo: Reuters

Investigators believe they have identified a suspect in the Boston Marathon bombing from security video and an official statement was expected later in the day, a US law enforcement source said yesterday.

However, no arrest had been made, three separate US government and law enforcement sources told Reuters.

Earlier yesterday, CNN reported that a suspect was in custody, citing law enforcement sources. But then the network cited three sources who said no one was under arrest after all.

The identification of a possible suspect marked the most significant publicly disclosed break since Monday’s blast at the marathon finish line killed three people and injured 176 others.

Investigators were also searching through thousands of pieces of evidence from cell phone pictures to shrapnel shards pulled from victims’ legs.

Based on shards of metal, fabric, wires and a battery recovered at the scene, the focus turned to whoever may have made bombs in pressure cooker pots and taken them in heavy black nylon bags to the finish line of the world-famous race watched by spectators.

Police search for clues in worst attack since Sept.11, 2001

A stretch of Boston’s Boylston Street almost a mile long and blocks around it remained closed as investigators searched for clues in the worst attack on US soil since the hijacked plane strikes of Sept. 11, 2001.

Cities across the United States were on edge after Monday’s blasts in Boston. Adding to the nervousness was the announcement that mail containing a suspicious substance was addressed to a lawmaker and to President Barack Obama.

The letter addressed to President Barack Obama contained a substance that preliminarily tested positive for the deadly poison ricin, authorities said yesterday.

News that the letter to Obama was being investigated came as a flurry of other reports of suspicious letters and a package caused the temporary evacuation of parts of two Senate buildings and set nerves on edge in Washington.

Law enforcement authorities reopened the Hart and Russell Senate buildings near the US Capitol after tests on various items showed there was no threat.

The suspicious letter to Obama contained “a granular substance that preliminarily tested positive for ricin,” an FBI statement said. It added: “There is no indication of a connection to the attack in Boston,” where three people were killed in bombings at the city’s marathon on Monday.

The Secret Service said the letter to Obama was received on Tuesday at a mail screening facility not located near the White House.

“The Secret Service is working closely with the US Capitol Police and the FBI in this investigation,” Secret Service spokesman Edwin Donovan said.

On Tuesday, authorities intercepted a letter sent to Mississippi Senator Roger Wicker that preliminary tests showed contained ricin.

The blasts at the finish line of Monday’s race injured 176 people and killed three: an eight-year old boy, Martin Richard, a 29-year-old woman, Krystle Campbell and a Boston University graduate student.