CHICAGO (CBS) — In the wake of the terror attacks in Paris, the FBI has acknowledged it is monitoring several individuals who are considered to have the potential to become homegrown terrorists.

Jay Abbott, FBI Special Agent in Charge for Indianapolis said, all over the country, the agency has stepped up surveillance of those with the potential to do harm to others.

“There are those who have risen to that threshold that we have cases on, like many other states,” Abbott told CBS 4 in Indianapolis. “We don’t just investigate people willy nilly, because they’ve exercised their right to free speech, or to assemble. There has to have been something that’s occurred that’s articulable that indicates they might want to act on those thoughts, and commit violence against somebody else.”

Abbott said it isn’t those being monitored who keep him up at night, but the potential terrorists they don’t know about, because the threat from home-grown extremists is much quicker and more unpredictable than before, so the FBI has less time to infiltrate extremist groups and prevent attacks.

“Now, it’s much much harder, because that planning period is so much shorter, and it goes from flash to bang so quickly,” Abbott said.

He wouldn’t say exactly how many individuals the Indianapolis office is monitoring, but said the FBI is doing such surveillance in every state.

Abbott said the FBI has warned local law enforcement agencies in Indiana and every other state that terrorists could try to carry out a Paris-like attack in the U.S., but he said the feds have no credible intelligence of an active threat.