The FBI says it is trying to determine who made online threats involving three commercial airline flights, causing the evacuation of two and the diversion of another.

FBI spokeswoman Laura Eimiller said Monday that agents were investigating whether the threats came from the same person or from copycats.

Law enforcement determined the public was not at risk.

Such threats are not rare. Eimiller said federal officials take them seriously and suspects can be prosecuted.

Passengers were taken from two planes that landed Sunday at Seattle-Tacoma International Airport. In addition, a Delta Air Lines flight was diverted to Dallas from its Los Angeles-Orlando, Florida, route.

The flights into Seattle originated in Long Beach, California, and Phoenix, and were operated by JetBlue and SkyWest.