Michael Trujillo came under scrutiny after sending a campaign e-mail that promised a "political bullet" for Huizar's opponent, Eagle Rock businessman Rudy Martinez.
Trujillo's controversial e-mail read:"Well, now he is going to be the dead rat he really is? We are about to put a political bullet in between Rudy Martinez's forehead and make him pee in his pants too."
Martinez filed a police report, accusing Trujillo of making criminal threats.
The district attorney's office said there was not enough evidence of an intentional threat to file charges.
Though Trujillo apologized for his remarks, Huizar still fired him after becoming aware of the situation.