Within minutes of the fatal bomb blasts at the Boston Marathon, self-described "truthers" erupted worldwide across the Internet with conspiracy theories about the crime.

Their efforts to find sinister machinations in the tragedy seem, well, conspiratorial.

Maybe it was that guy supposedly spotted on the roof overlooking the marathoners’ route, or disgruntled taxpayers, or the writers of the animated TV series "The Family Guy," or, of course, the federal government running another "false flag" operation to seize people’s civil rights.

Front and center is conspiracy entrepreneur Alex Jones. An Austin, Texas-based writer, radio talk-show host and owner of the conspiracy site Infowars.com, he says the Newtown, Conn., elementary school massacre was a government plot. Within hours of the Boston explosions, Jones used a "falseflag" hashtag on Twitter to say: "Our hearts go out to those that are hurt or killed at the Boston marathon — but this thing stinks to high heaven."

Another conspiracy writer attended Massachusetts Gov. Deval Patrick’s morning press briefing today in Boston to ask: "Is this another false-flag attack staged to take our civil liberties?" He was dismissed with a perfunctory "no."

A false flag, which was first a trick by 18th-century naval captains who’d hoist flags of other nations when approaching an enemy vessel, now is used to describe an attempt to hide the identity of the person or group responsible for an operation.

Mike Adams, of the Internet site Natural News, suggested the "official story" of the Boston bombing is unraveling quickly.

”It’s now becoming clear that members of the Boston bomb squad had advanced notice of the horrific bombing," Adams wrote. "Bomb-sniffing dogs were present at the start of the race and the finish line, even before bombs went off."

Such security precautions have become common for major events like the Boston Marathon in the aftermath of the 9/11 attacks. But those attempts to thwart terrorism seem sinister to increasingly sophisticated paranoia promoters.

”I can’t say that more people believe in conspiracy theories these days," concluded Mark Fenster, author of the book "Conspiracy Theories: Secrecy and Power in American Culture" and a University of Florida law professor. "But now there is more of an organized commercial structure to this. Folks are going to jump right in and find a conspiracy theory."

Theories over who was responsible for the Boston bombings covered an astonishing range and showed considerable imagination.

— A blurry digital photo of a man walking on a rooftop overlooking the marathon course went viral, prompting wide speculation that it depicted the bomber.

— Is it coincidence that a recent episode of Fox TV’s "Family Guy" animated series showed the main character detonating bombs and winning the BostonMarathon by killing other runners? It was "a chilling reminder of the very real scenes of carnage we saw," wrote Paul Joseph Watson for Infowars.com. YouTube today took down a clip from the episode called "Turban Cowboy." ”Family Guy" creator Seth MacFarlane tweeted that it was edited to tie the bomb to the marathon, which he called "abhorrent."

— What about Wall Street? "The price of gold and stocks plummeted earlier in the day before the explosion occurred, which is a weird coincidence," blogged Ms. Wanda, who otherwise did not identify herself.

— Don’t forget the North Koreans. "I hope everyone realizes this is a perfect false flag for martial law," wrote "Just Another Day" on a conspiracy website. "I would not be surprised if a member of our government made a deal with the loose cannon in North Korea."

— Even mainstream media commentators couldn’t resist noting that the Boston attack occurred on Tax Day, which "does cause some emotions around the country, sometimes in the wrong parts of the brain," Chris Matthews said on MSNBC.

But the most consistently touted theory focused on a government conspiracy.

”Evidence is beginning to emerge suggesting that the act may have been a false flag attack," wrote Brandon Turbeville for Activist Post. "The Boston bombing carried the trademark ‘coincidence’ of a (bomb squad) drill scheduled to take place at almost exactly the same time that the bombs were being detonated at the marathon."

Some people are fighting back against the conspiracy barrage. Jaimie Muehlhausen of California registered the Internet domain "bostonmarathonconspiracy.com" to "keep some conspiracy theory kook from owning it," he wrote on the website. "Please keep the victims of this event and their families in your thoughts."

”I did this out of respect for the victims and the families of those affected by this horrible tragedy," Muehlhausen said in an email. "I did this as a private citizen and have no ulterior motives or business angles to it. Just trying to do the right thing."

The site, accessible much of today, had gone blank by late afternoon. A conspiracy?