ATLANTA -- The FBI is actively trying to find those responsible for recent online airline bomb threats.

On Saturday, two planes were escorted to the airport by NORAD jets to Hartsfield-Jackson Atlanta International Airport after someone made threats on Twitter.

Both planes were searched and no explosives were found.

The FBI tells said it's up to the airlines to determine if a threat is credible, whether It comes from social media or elsewhere. In Saturday's case, both bomb threats were deemed credible and that's why the FBI was called in to investigate.

Cyber attack expert GregoryEvans believes the FBI knows who is behind KingZortic, the username responsible for the threats.

"Right now we are focusing on who it was, where it was and how we can best lay hands on them," said FBI Special Agent Stephen Emmett.

The FBI says the person responsible for the threats could face serious federal charges, such as conspiracy to destroy an aircraft.

"I have the utmost confidence in our investigators, that work these problems," Evans said. "They are very good at it, and they have a lot of tools needed for this investigation."

Airline officials said whether the threats are a hoax or real, whoever did it should be held responsible.