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President Obama鈥檚 brief statement Monday evening on the deadly bombings that struck near the finish line of the Boston Marathon earlier in the day gave few clues concerning the investigation into the attacks.

But three themes the president homed in on are likely to echo through the days ahead. Boston is a resilient city and will overcome this tragedy, no one should rush to conclusions about who is behind the attack, and whoever did it will be found out and will be 鈥渉eld accountable.鈥�

Terrorism experts said the attack, which killed three people and left more than 100 injured, some critically, had some of the hallmarks of a 鈥渓one wolf鈥� or perhaps an ad hoc domestic group 鈥� but that it was also way too early to rule out individuals or a group affiliated or inspired by Al Qaeda or one of its regional organizations.

鈥淭his [attack] has some of the ring of Al Qaeda, but it also has the earmarks of a lone wolf,鈥� says Juan Zarate, a former deputy national security adviser for combating terrorism under President George W. Bush.

The symbolism and high visibility of the Boston Marathon finish line are reminiscent of Al Qaeda targeting, he says, but other factors 鈥� that the attack was carried out on April 15, the federal income tax deadline and what in Massachusetts is Patriot's Day 鈥� could also suggest the work of a disgruntled lone wolf or domestic antigovernment groups.

National security analyst Peter Bergen said on CNN that the attack could be the work of 鈥渞ight-wing extremists.鈥� For the so-called patriot groups, anything from tax day to the heated national debate on gun regulations could have been the triggers for such an attack.

Some analysts even noted that the attacks were carried out at about the 26-mile marker of the race 鈥� which had been dedicated to the 26 victims in Newtown, Conn., which has moved to the center of the gun-regulation debate.

But for Mr. Zarate, now a transnational threats and homeland security expert at the Center for Strategic and International Studies in Washington, other recent terror attacks or thwarted attacks also serve as reminders that this could have been perpetrated by several groups 鈥� or individuals.

The 2011 鈥渓one wolf鈥� terrorist attacks in Norway, which targeted both government buildings and a summer youth camp, are evidence that individuals can plan and implement major attacks.

The Norway attacks, carried out by Norwegian right-wing extremist Anders Breivik, are also a reminder that initial speculation is often wrong: In that case many officials and experts initially assumed the attacks were the work of international terrorist groups.

Officials in Boston said there was no intelligence or 鈥渃hatter鈥� hinting at a possible marathon attack. That bit of information suggested to some experts that the attack may indeed have been the work of a lone wolf or a lone wolf 鈥減ack.鈥�

Yet while that might initially 鈥渟uggest this was not the work of a network,鈥� Zarate says, he also cautions that the thwarted New York City subway bombing plot of 2009 and the failed Times Square bomber of 2010 were not foiled because of network 鈥渃hatter鈥� before the planned attacks.

鈥淚f you listen to the instructions going out from a group like Al Qaeda in the Arabian Peninsula, the focus is on attacking in place鈥� without waiting for instructions from the top, Zarate says. 鈥淭he message is, 鈥楧on鈥檛 wait for Al Qaeda central, and don鈥檛 wait necessarily to hit spectacularly鈥� 鈥� like 9/11, 鈥� 'But hit and hit hard.鈥� 鈥�

Public safety officials in Boston reported Monday evening that one individual, a Saudi national at the marathon finish line, was questioned but was not a suspect. Authorities also said they were searching for a van that was seen in the area before the blasts.

Nationally, security measures were tightened in New York, Los Angeles, and Washington 鈥� where the pedestrian street in front of the White House was closed. Increased security was also ordered in London, which is set to hold its own marathon race Sunday.聽

The Federal Aviation Administration issued a 鈥済round stop鈥� or temporary flight restriction on Boston鈥檚 Logan International Airport after the blasts, but the restriction was lifted within a few hours.

Mr. Obama said Boston, local investigators, and those attending the wounded and families of the victims could count on the full support of the federal government. He also said that 鈥渢he American people will be saying a prayer for Boston tonight.鈥�

Most questions about the attack remain unanswered, he said, but he said officials will 鈥渇ind out who did this, and why they did it,鈥� and that 鈥渢hey鈥� would then be held accountable to the full extent of the law. 聽聽