Kyle Bangayan was taken into custody at his parents' Los Angeles apartment in the Little Armenia area on Sunday at about 11 a.m. The LAPD and the FBI responded to threats that Bangayan allegedly posted on Facebook using an alias.
Police say he threatened to carry out shootings at multiple elementary schools in the Los Angeles Unified School District while referencing the massacre in Connecticut.
"He was clear in his statements, and his abilities matched those statements," said LAPD Chief Charlie Beck during a news conference.
But according to a spokesman for the district attorney's office, the charges were declined because there was no specific threat to a victim or school. The FBI also decided not to pursue the case either.
At the apartment, authorities found nine firearms, including rifles, handguns and a shotgun, along with ammunition. It was unclear whether the weapons were purchased legally or who they were registered to.
Chief Beck said Los Angeles police would begin being present every day at every elementary and middle school in the city.