A search of his otherwise empty apartment in suburban Inglewood turned up a note containing unspecified threats that cited Wednesday's Sept. 11 anniversary. Additional details of the contents of the letter were not immediately provided.
No harmful materials were found at the airport or the man's apartment, the FBI said.
The Los Angeles Police Department Bomb Squad also inspected a package allegedly left at TSA's headquarters in the airport after he resigned from his job, and the package was addressed to another agency employee, officials said.
The officers found no harmful contents in the package but turned up an eight-page letter in which Onuoha expressed disdain for the United States and referenced an event that led to a recent suspension from the job he had held since 2006, the FBI said. It was not clear early Wednesday what the incident had been.
Later, a man authorities believed to be Onuoha made two phone calls to TSA saying certain airport terminals should be evacuated. During one call, the man told an employee he would be monitoring to see if authorities would evacuate the terminals as instructed.
No threats were found in authorities' search of the terminals. The airport is the nation's third busiest airport, according to its website.
A request for comment from the airport was not immediately returned early Wednesday.