The harshest attack against Mitt Romney to yet hit the South Carolina airwaves is coming not from his GOP rivals, but from comedian Stephen Colbert  , whose Super PAC is up with a 60-second spot accusing Romney of being a "serial killer."

The harshly-worded ad spares no drama, showing a butcher carving up a carcass and a limp pair of feet being ominously dragged around a dark corner. But coming from the Comedy Central funnyman, the ad seems more like a tongue-in-cheek jest than a legitimate character attack.

"Mitt Romney has a secret," says the narrator, John Lithgrow, who played a serial killer on the Showtime series "Dexter." "As head of Bain Capital he bought companies, carved them up, and got rid of what he couldn't use. If Mitt Romney really believes 'corporations are people, my friend' then Mitt Romney is a serial killer. He's Mitt the Ripper."

The ad is airing on the CBS station in Colbert's hometown of Charleston, South Carolina and comes just days after Colbert transferred control  of his PAC to fellow comedian Jon Stewart and announced he would launch an exploratory committee to find out "if there's a hunger" for him to run for president in South Carolina.

The pro-Colbert PAC,  Americans for a Better Tomorrow, Tomorrow, spent $7,600 to air the ad 11 times on CBS Charleston.  Beginning last Sunday , the ad will air twice per day until Thursday, once during the morning news and once during the nightly news, said CBS affiliate WCSC's General Manager Rita Scott.

So far the station has heard no complaints about the "serial killer" ad, Scott said.

In an interview with George Stephanopoulos Sunday on ABC's This Week Colbert claimed he had not seen the ad.

"I had nothing to do with that ad. I have no control over that ad," Colbert said. "I am not calling anybody a serial killer. I can't tell Americans for a Better Tomorrow, Tomorrow what to do. It's not my super PAC."

Compared to the $10.2 million that current GOP candidates and Super PACs have spent on ads in the Palmetto state, the pro-Colbert PAC's $7,600 ad buy is mere pennies. But in a race where negativity seems to be the new norm, the commercial's over-the-top "serial killer" accusation falls in the same vein as the top candidates' ads.

Most notably, the pro-Gingrich Super PAC Winning Our Future launched an ad calling Mitt Romney a "corporate raider" for his work at Bain Capital. Gingrich has tried to distance himself from the ads, noting that he is forbidden by law from coordinating with the PAC, and calling for the group to remove any untrue statements in the ads. Colbert is employing the same line.

"If that's not accurate, I hope they take it down," Colbert said Sunday. "I don't know if Mitt Romney is a serial killer. That's a question he's going to have to answer. I do not want any untrue ads on the air that could in any way be traced back to me."