The bomb attacks in Boston taught us that America's enemies are poised to strike at any time and that the two brothers didn't fit the typical profile of a terrorist.
"A terrorist can be anyone, look like anyone," said Hanan Yadin, a former member of Israel's secret service.
They live among us in secret, hiding and waiting.
"They are clearly being radicalized in this country," said Joan Neuhaus Schaan, a local terrorist analyst.
Houston is a prime example. Aafia Siddiqui, also known as lady Al-Qaeda, the underwear bomber Umar Farouk Abdulmutallab, Daniel Maldonado, Adnan Mirza and American citizen Kobie Williams are all radical extremists with ties to Houston.
"Individuals that can come and go freely from the United States because of their visas or citizenships are highly prized by terrorist organizations," said Neuhaus Schaan.
Since the mid 1980s, terrorists have come to Houston to live and to get an education.
"You find college graduates. You even find Ph.D.s," said Neuhaus Schaan.
In the case of a Pakistani national and an American citizen, they came to the Houston area to practice for war. These radical extremists living among have changed their tactics and counterterrorism experts said it's no longer about what someone looks like. It's about their behavior. Over the past two decades, terrorists have done their best to blend into Western society, learning our language and culture.
"We need to look for different signs, such as what is a suspicious package? What is a suspicious person?" said Yadin.
Even though we are constantly being told to be vigilant, to say something if we see something suspicious, what is "strange"? Experts said Americans don't understand how to define this word in terms of possibly terrorist activity. For example, it's not unusual to see someone take photos or videos in public, but when someone tries to conceal their activity or focuses on details like security cameras or restricted areas, that's suspicious behavior. Though reporting it remains a delicate balancing act.
"The political correctness top cover is making the situation worse," said Neuhaus Schaan.
The federal government continues to put out videos to try to teach us to look beyond common stereotypes and to focus on the actions, not the person.