Highlights from President Obama’s speech in Newtown, Conn., after the Sandy Hook elementary school shooting tragedy. (The Washington Post)

New threats and false alarms rattled police departments and schools around the country on Monday, the first, jittery school day after Friday’s mass shooting in Connecticut.

In Los Angeles, police said Monday that they had arrested a 24-year-old man for allegedly making threats on Facebook. Police said Kyle Bangayan had referenced the rampage in Newtown, Conn., but had not mentioned any specific school as the target of his alleged threats.

Bangayan was arrested Sunday, police said, at his parents’ home in Los Angeles. They said nine guns, including rifles and a shotgun, were seized at the home.

Elsewhere, the Associated Press reported that three school districts near Newtown went into lockdown Monday after someone reported a suspicious person at a nearby train station. The alarm was lifted about two hours later.

At Upper Dublin High School near Philadelphia, officers rushed to campus after security officers mistook a student’s umbrella for a gun. And in Tampa, the Hillsborough County sheriff’s office questioned students after a bullet was found on a school bus, the AP reported.

Majority sees Connecticut shooting as societal problem