The 'Anger Management' star - who recently claimed his nine-year-old daughter, Sam, was "bullied out" of Viewpoint School in Calabasas, California and encouraged his Twitter followers to smear the campus with "rotted egg, a roll of toilet paper, or some dog s**t" - accused supporters of the school of leaving a threatening note and a knife jammed into a tree outside his ex-wife Denise Richards' home.
The 49-year-old actor told TMZ Live that his daughters "had the pleasure of discovering a steak knife used to nail a note to the tree", after calling in to explain his latest Twitter rant on Monday during which he wrote: "Here's why people suck; a group of mindless Viewpoint [School] supporting doosh-bagz have targeted [Denise] and the girls with 'bullying tactics' as a response to my call to arms."
He also urged people to leave his family alone, writing: "Leave them alone. This is not a threat but a promise that justice will be served. I'm not hiding. You are. Show yourselves you spineless cowards. Oh that's right; cockroaches scatter in the light."
Charlie said two people were captured on surveillance tape outside the property leaving the note and the knife and he has contacted police to investigate the alleged threat.
He wrote: "FYI - we have your faces on camera. Police are involved."
Last week the outspoken star - who also has daughter Lola, seven, with Denise, four-year-old twins Bob and Max with former spouse Brooke Mueller and adult daughter Cassandra with ex-girlfriend Paula Profit - appeared to single out a nine-year-old child Victoria for causing Sam to have to leave the school last year.
The school denied his claims and insisted it did everything necessary to deal with the situation.