American authorities are questioning a person in connection with the discovery of box cutters and other suspicious items on two Southwest Airlines jets.
But the agency's director, Robert Mueller, said yesterday's incident, which triggered an alarming order for US airlines to conduct prompt and detailed searches of their aircraft, did not appear to be a "terrorist event" and there was no "imminent threat."
An FBI statement later in the day said law enforcement and transportation security officials had "located and interviewed" an individual believed to be responsible.
"Based upon the investigation conducted thus far, this individual does not appear to pose any further threat to airline security," the FBI statement said.
Although the agency noted the investigation was continuing and did not announce any charges in the case, it did say the matter was expected to be addressed Monday in federal court in Baltimore.
While authorities would not identify the person who was questioned, a source close to the matter said law enforcement had interviewed a 20-year-old man, believed to be a college student.
Southwest, a major presence at Baltimore-Washington International airport, said in a statement it had been told the man was not connected to the airline in any way.
The Transportation Security Administration, the government agency responsible for airline security, said it had linked an email it received last month about aviation security to the case and had been investigating the individual who was questioned for several months.
Box cutters, bleach, matches and modelling clay simulating an explosive were discovered by Southwest employees late on Thursday in plastic bags on the two Boeing 737 planes in Houston and New Orleans.
Southwest said notes accompanying both packages indicated the items were intended to challenge TSA airport security procedures, which are under close scrutiny by congressional lawmakers troubled by reports of gaps in screening of passengers and bags and airline and airport workers.
The suspicious items in New Orleans were found in a bathroom compartment of a plane Southwest said had come from Orlando, Florida. The airline said a similar discovery was made on the plane in Houston. Both were found during maintenance.
"I will tell you that it does not appear to be a terrorist event and there is no imminent threat." Mueller told reporters in Houston. "There were no explosives, there was no imminent threat in terms of a capability to commit a terrorist act."
Box cutters were used as a weapon by the September 11, 2001, hijackers and have since been banned as carry-on items. Liquid bleach is not permitted on commercial flights, but some matches and clay are allowed, according to the TSA.