NEW YORK -- The FBI investigated suspected New York and New Jersey bomber Ahmad Khan Rahami two years ago, but he was not considered a threat. This is not the first time someone “known” to investigators is accused of a terrorist act.

As Rahami’s case moves forward, federal agencies are working to keep up with what former FBI agent Manny Gomez calls a tsunami of potential threats.

“The FBI does not have the resources both legally, and in terms of manpower and funding. These people are being radicalized quicker than we can identify them.”

In Rahami’s case, despite his father calling him a terrorist in 2014 and his year-long stay in Pakistan, an FBI source says at that time it found nothing in its “indicators” -- such as links to other known terrorists or radicalized behavior -- to point to Rahami being a terror threat.

Since 9/11, the Homeland Security Committee says “there have been at least 166 homegrown jihadist plots in the United States, including attempts to join terrorist groups overseas and execute attacks at home.” That’s an average of 11 per year.

Just this year alone, 26 people in the U.S. have been arrested in 13 states for ISIS-related activities including “plots to attack,” “financial support,” and “weapons charges.”

Sometimes there are clues, but to make a case authorities need evidence that they often do not find.

The Orlando Pulse nightclub shooter, Omar Mateen, had been on the FBI’s terrorist watch list for ten months and was investigated, but later removed from the list. In June, he killed 49 people.

CBS News consultant Fran Townsend says the system needs improvement.

“You want the terrorist watch list to be over-inclusive. So that if there is somebody that you think may be [a threat], but you don’t have enough, you want to alert other agencies to put more information in that may push you over the edge.”

Since 2014, authorities have arrested 105 people in the U.S. They say those people were plotting attacks, attempted to join ISIS, or provided money, equipment or weapons to that terror group.