Terrorism and political violence expert Mark Ensalaco worries the Boston bombings are similar to the Oklahoma City and the Atlanta Olympics.

University of Dayton terrorism and political violence expert Mark Ensalaco worries the bombings at the Boston Marathon Monday are acts of domestic terrorism.

"My immediate reaction is this is something similar to Oklahoma City and the Olympics in Atlanta," said Ensalaco, who has studied political violence and terrorism for more than 25 years.

"Because it's tax day and a holiday in Boston honoring revolutionaries who fought for America freedom, and many people from foreign nations were in attendance, I worry a right-wing extremist used a highly visible event such as the Boston Marathon to make a highly visible statement."

Ensalaco stresses it's still early in the process and there needs to be more investigation. Al-Qaida remains a possibility, he said, but this attack doesn't follow al-Qaida's blueprint.

"Al-Qaida does suicide bombings. They run into large crowds, such as one that would have been at the start line and blow themselves up," said Ensalaco, author of Middle Eastern Terrorism: From Black September to September 11.

If indeed the Boston bombings are the work of domestic terrorists, how could something like this elude counter-terrorism efforts?

"The fact of the matter is we monitor al-Qaida closer than we do these domestic groups," said Ensalaco, who has discussed terrorism and international issues with CNN, CBS Radio News, The Associated Press and Reuters, among others.