Boston attack: Swath of city on lockdown as police scour for additional bombs

State and city authorities are treating Boston as a city under attack.

After two explosions that killed two and injured dozens more near the Boston Marathon finish line, the city shifted in a heartbeat Monday from a festive day of sport to a lockdown environment. Police were seeking to protect marathon spectators and residents against the potential that additional bombs might go off.

“We are stabilizing the situation,” Boston Police Commissioner Edward Davis said during a press conference about two hours after the blasts, which occurred at 2:50 p.m. 

“We are asking that people stay out of crowds and calmly make their way home,” Gov. Deval Patrick said at the news conference.

Commissioner Davis described the situation as “an ongoing event,” implying the risk of further bomb attacks after the two that rocked the finish line in quick succession.

In the initial confusion of the day, it appeared as Davis spoke that another explosion may have already happened. The commissioner said officials were treating an incident at the John F. Kennedy Presidential Library, in the Dorchester neighborhood several miles from the marathon finish line in the Back Bay, as potentially related to the other explosions.

According to subsequent news reports, what occurred at JFK Library was a fire in a mechanical room. The cause remains unknown.

Authorities around the city are active Monday evening on multiple fronts: checking the marathon course and other areas for explosives, tending to the injured, helping people who are trying to locate loved ones, and launching an urgent hunt for whomever set the explosives.

Mayor Thomas Menino gave out a hot line for people trying to find the whereabouts of loved ones: 617-635-4500. And a Google people-finder site has been set up for the same purpose.

Separately, law enforcement officials said people should call 800-494-TIPS with any tips related to the crime.

With the two explosions in close proximity to each other, and the possibility that the JFK library incident may be linked to the bombings, the possibility rises that the perpetrators planted other explosives across a much wider area, say homeland security experts. Indeed, another device was discovered and exploded by authorities Monday.

Against that possibility, Boston authorities shut down cellphone tower service in the city to guard against bombs that could be triggered by cellphone, a common terrorist tactic.

Federal and state authorities have kicked into high gear, with federal agencies deploying investigative teams. The FBI has a big field office in Boston, and because this was an attack of some scale, a variety of key agencies are nearby.

While there is little to go on at this point, the fact that the Back Bay explosions did not destroy buildings nearby indicated that they were relatively small-charge bombs.

“What we saw today was a relatively small-scale set of explosions,” says Stephen Flynn, co-director of the George J. Kostas Research Institute for Homeland Security at Northeastern University, in Boston.

“The challenge with these smaller-scale attacks is that they are much harder to detect in the early stages – precisely because they don’t require much sophistication, planning, or leadership, funding, or financing,” he adds.

The more sophisticated an attack, the more ambitious, and the more requirement for movement of money and safe houses for operatives and communications, all of which can hit FBI and other tripwires, says Dr. Flynn.

“The smaller-scale attacks like this require much less coordination, resources, and people – so it’s more difficult to ensnare them in their preparation stages,” he notes. “Still, this is clearly more than a 'lone wolf' attack. We may be dealing with a small group of people, perhaps three or four people, but not the type of thing we saw after 9/11 – discovering [Al Qaeda leader Osama] bin Laden and a large group of operatives coming in from far away.”

President Obama was cautious about describing the attack, not using the word terrorism but implying that it could have been perpetrated by a group rather than a lone individual.

“We still do not know who did this or why,” Mr. Obama said in televised remarks just after 6 p.m. “But make no mistake, we will get to the bottom of this.” He said that "any responsible individuals, any responsible groups will feel the full weight of justice.”

Similarly, Davis of the Boston Police said, “we’re not being definitive” about the word terrorism. “You can reach your own conclusions,” he added in his initial press briefing of the afternoon.

Obama noted that the attacks took place on a day when runners from around the world put Boston in the global spotlight, and on a state holiday – Patriots Day – that celebrates the idea of liberty.

According to news reports, the number of people injured in the two finish-line blasts approached 100.

“On days like this, there are no Republicans or Democrats. We are Americans united in concern for our fellow citizens,” Mr. Obama said. He said all Americans would "say a prayer for Boston."

The attack in Boston prompted heightened security in other cities.

New York Mayor Michael Bloomberg issued a statement confirming the "stepped up security" at what he termed "strategic locations and critical infrastructure, including our subways." Mr. Bloomberg said some of the deployments would be noticeable, such as bomb-hardened vehicles, and other steps might be less noticeable. All 1,000 counterterrorism police as well as the entire NYPD "are being fully mobilized to protect our city," he said.

The Associated Press reported that in Britain, police are reviewing security plans for Sunday's London Marathon. And some major airports as far away as California ramped up their vigilance against possible threats.

Staff writer Ron Scherer in New York contributed to this report.