PHOENIX - The retired FBI agent who wrote the so-called Phoenix memo, about Middle Eastern men taking classes at American flight schools before the 9/11 terrorist attacks, is speaking out about the recent terrorist attack in New York.

“I was not surprised that it happened,” Ken Williams told 12 News. “It's a very cheap and easy way to commit murder. I'm surprised it hadn't happened beforehand.”

Williams would know. The retired FBI agent was based in Phoenix for 30 years and chased terrorists around the world. He's also known for authoring the Phoenix memo, a report written two months before the 9/11 attacks. In it, Williams raised concerns about Middle Eastern men attending U.S. flight schools, including some in Arizona.

“Since 9/11, the enemy has changed the way we, as Americans, have to think,” Williams said. “You always have to be cognizant of your surroundings. When you're in a large group or a large crowd, you always have to be looking around your back, you don't feel comfortable.”

In the last two years, there have been almost two dozen attacks where terrorists have used vehicles to ram people. This includes the scene in Nice, France, where 86 people died and more than 450 others were injured.

“It's a very easy thing to pull off,” Williams said. “It's a cheap way to do things.”

And as for predicting these kinds of attacks, “It's extremely difficult,” Williams said.

He said one of the only ways law enforcement can prevent vehicle-type attacks, is for others who notice something suspicious to speak-up. It's the saying, “See something, say something.”

“We're not going to be able to prevent everything,” said Williams. “And the quicker people know that, the better off. They (terrorists) have to be right once. We (law enforcement) have to be right all the time to prevent it."

Williams said the FBI would be better able to keep Americans safe if it had a bigger budget and could hire three times the number of agents it has now.