Johnny Carson (search) was a barrel of laughs on TV, but fear stalked him off the set with wacko after wacko threatening to murder the King of Late Night, FBI documents reveal.

For more than a decade, Carson was dogged by a terrifying series of letters that told him he'd be shot dead, blown up or otherwise assassinated, according to the agency's file on the threats obtained by the syndicated show "Inside Edition."

In one chilling missive sent in 1976, the writer demands $6,000 from Carson or "I will kill him."

The warning contains a photo of Carson and an unidentified woman with bullet holes through their heads.

In a 1974 note, a North Carolina man, not identified by the FBI, demands $50,000 from Carson, telling him: "I have nothing to lose ... I will be in Hollywood to carry out the threat if the money is not sent. P.S. How is your wife — I'm a homicidal maniac."

Others didn't demand money from the legendary "Tonight" show host — they just wanted him dead.

In 1975, a "Victor Lake" tells Carson he's joined the Weather Underground and will blow Carson to smithereens.

"If I were you, I'd maintain a ceaseless search for bombs. I'm meaning: every single day, sadistic swine."

Most threats were sent to Carson's office at NBC, but one particularly unsettling one was a 1973 telegram to his sidekick Ed McMahon.

"Dear Ed, Stick close to your boss tonight. He might need your help ... [Signed] a bereaved friend," it reads.

In a nod to McMahon's well-known love of booze, a P.S. notes: "I was planning to send a hundred years old bottle of scotch but they can't transmit it over the wires."

The 399 pages of documents obtained under the Freedom of Information Act are part of a 615-page file the FBI kept on the dozens of threats against Carson from the 1970s and '80s.

They reveal that then-FBI Director William Webster was in contact with Carson, but it's unclear how many letter-writers were caught.

In one FBI memo, Carson's lawyers are concerned about publicity from one of his upcoming divorces because news about the entertainer's private life usually increased the number of threats.

The four-times married Carson, who died last January at 79, never spoke of the threats in public.

The "Inside Edition" segment airs Friday.

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