Luna did not detail what the writings contained, but said it was being reviewed by the FBI. A motive for the attack remains unknown.
"The manifesto that we received from this individual was sent to our partners at the Federal Bureau of Investigation. They're still analyzing it to try and figure out what happened, why it happened," Luna said. "I don't know if we'll ever have a motive, but we continue to try."
Luna made the remarks during an event marking six months since the attack. Rep. Judy Chu, who represents the district that includes Monterey Park, also announced a legislative package in coordination with New York Sen. Kirsten Gillibrand, to try to reduce gun violence through red flag laws.
RELATED: Rep. Judy Chu introduces 2 bills to utilize red-flag laws on 6-month anniversary of Monterey Park shooting
Rep. Judy Chu introduces 2 bills to utilize red-flag laws on 6-month anniversary of Monterey Park
The shooting occurred during Lunar New Year celebrations in Monterey Park. The gunman, 72-year-old Huu Can Tran, killed 11 people and was found dead in a white van the next day of a self-inflicted gunshot wound, authorities said.
The shooting inside the Star Ballroom Dance Studio is the deadliest mass shooting in L.A. County history.
The building that housed the Star Ballroom remains, but it's unclear what, if anything, will ever occupy the space.
The CNN Wire contributed to this report.