A man looks down Boylston street towards the finish line of the Boston Marathon in Boston on April 17, 2013. The investigation of the Boston Marathon bombing is focusing on a suspect or suspects believed to have carried heavy bags or backpacks, but entered a third day on Wednesday without any arrests or word on who was responsible. REUTERS/Shannon Stapleton
BOSTON — Investigators have spotted a Boston Marathon bombing suspect from security video taken before two blasts ripped through central Boston on Monday, a U.S. law enforcement source said on Wednesday, in what is potentially the biggest break in the case yet.
No arrests had been made, and the suspect in the video had not been identified by name, two U.S. government officials said.
Police considered making an appeal to the public for more information at a news conference, a U.S. government source said, but the FBI canceled that news conference after delaying it several times, Boston police said.
The explosions at the Boston Marathon finish line killed three people and injured 176 others in the worst attack on U.S. soil since Sept. 11, 2001.
The bombings, as well as subsequent reports that someone tried to mail the deadly poison ricin to U.S. President Barack Obama - the second report of such a letter in two days - have created a climate of uncertainty in the country.
Nerves were jolted further by an inaccurate report on cable news network CNN that a bombing suspect had been arrested.
Shortly after CNN retracted its report of an arrest in the case, security officials at Boston's federal courthouse ordered staff, media and attorneys to evacuate due to a bomb scare that was later found to be a false alarm.
In Washington, authorities were investigating a letter addressed to the president after the contents preliminarily tested positive for ricin. Authorities had intercepted a similar letter sent to Republican Senator Roger Wicker of Mississippi on Tuesday.
The FBI said late on Wednesday it had arrested Paul Kevin Curtis, of Corinth, Mississippi, in connection with the letters.
Earlier the agency had said there was no indication of a connection between the ricin letters and the Boston bomb attacks, but they reminded Americans of anthrax mail attacks the country in the wake of the Sept. 11 attacks 12 years ago.