MIAMI -- A plane returned to Miami International Airport after a questionable note was found on board.

American Airlines Flight 1640 was headed to Boston from Miami.

Once the Boeing 757 was in the air, a flight attendant found a note with the word "bomb" written on it in one of the bathrooms. The crew made the decision to return to Miami.

"The plane was put in the penalty box and all passengers disembarked and were re-screened, as well as all the luggage," said FBI Investigator Judy Orihuela.

At around 2 a.m., Orihuela said she received an e-mail that Miami-Dade Police cleared, TSA had rescreened and everything was ok.

Crew and passengers were scheduled to depart for Boston Friday morning.

Miami-Dade police were processing the note at their lab. The investigation continues.