US police believe video may identify bomber

Investigators in the Boston Marathon bombings believe they may have identified a suspect from security video footage but dismissed reports that an arrest had been made.

Law enforcement officials have been trawling surveillance videos from shops and businesses, and camera footage from spectators and television crews searching for clues to identify who planted two bombs that exploded near the marathon’s finish line, killing three people and wounding more than 170.

The possible identification of a suspect was the first breakthrough in the investigation into the worst attack on US soil since the September 2001 attacks on New York City and Washington DC.

Boston Police and the FBI denied media reports on US television news channel CNN and the Associated Press news wire that a suspect had been taken into custody. The FBI urged the media to exercise caution in their coverage and verify information through "appropriate official channels before reporting".

The FBI postponed a press conference yesterday evening at which officials had been expected to give an update on the investigation. The briefing had already been rescheduled from an earlier time.

The US attorney’s office in Boston said it was postponed due to activity at a federal courthouse in the city where police and reporters had gathered earlier amid confusion over whether a suspect had been detained.

As the Boston investigation made slow progress, law enforcement officials in Washington said that preliminary tests carried out on a letter sent to President Barack Obama contained poisonous ricin, while suspicious packages discovered in the US Capitol led to the shutdown of parts of two Senate office buildings.

The letter addressed to the president was discovered a day after a Republican senator from Mississippi also received a suspicious letter.

The packages raised fears and intensified security efforts in a US capital already on edge after the bombings. The FBI said that there was no connection between the letters and the marathon blasts.

The investigation in Boston is focusing on who may have planted homemade bombs made out of pressure cooker pots and shards of metal, nails, “BB” pellets and ball-bearings planted in black nylon bags. The crudely designed bombs were designed to inflict maximum casualties in the crowd by exploding shrapnel.