Homeland Security Secretary Jeh Johnson on Wednesday warned that the Boston Marathon bombing may be a sign of things to come as the U.S. attempts to defend itself from terrorist attacks.
"I think the Boston Marathon bombing maybe a sign of the future. And in many respects those threats are harder to detect," Johnson told the House Homeland Security Committee. "I am also concerned about those who self-radicalize ... about the so-called lone wolf."
Specifically, Johnson was referring to individuals who work alone to plan or carry out a terrorist attack without instructions from a terrorist organization. Officials have said that with the rise of the Internet a person can "radicalize" without traveling to a country where a terrorist group is active.
The alleged Boston Marathon bombers, Dzhokhar and Tamerlan Tsarnaev, are considered "lone wolves" because they allegedly planned and carried out the attack on their own, rather than with the support of a broad network such as al-Qaida.
Johnson said his department must continue to boost its ties with state and local officials "to address the threats we face from those who self-radicalize to violence, the so-called lone wolf who may be living quietly in our midst, inspired by radical, violent ideology to do harm to Americans -- illustrated last year by the Boston Marathon bombing."
The April 2013 bombing killed three people and left at least 260 injured. The trial for one of the alleged bombers, Dzhokhar Tsarnaev, is expected to start in November.
"We've got to be vigilant. I think the terrorist threat is becoming more diffuse," Johnson said.
His comments echo those made by FBI Director James Comey, who has repeatedly warned of the offshoot of al-Qaida-aligned groups, radicalization within the United States, and the potential threat from Americans and Europeans who have traveled to Syria and possibly been recruited by terrorist groups to carry out attacks back in their home countries.
"We have to be constantly vigilant in looking out for those efforts and preventing them," Johnson said in response to questions about Syria becoming a breeding ground for terrorism because it has large ungoverned areas.
Committee Chairman Michael McCaul noted that "the events in Syria are now threatening to become issues for us at home."
Johnson was confirmed to DHS's top spot in December with bipartisan support. During the confirmation process he named morale, leadership vacancies, and terrorism as his top concerns.
Secretary Jeh Johnson said the U.S. faces an increasing threat from homegrown, "lone-wolf" terrorists.