This article was written by CBSNews.com's Tucker Reals.
Hours before London explosives technicians in the heart of the British capital's tourist-rich theater district, a message appeared on one of the most widely used jihadist Internet forums, saying: "Today I say: Rejoice, by Allah, London shall be bombed."
CBS News found the posting, which went on for nearly 300 words, on the "al Hesbah" chat room. It was left by a person who goes by the name abu Osama al-Hazeen, who appears regularly on the forum. The comment was posted on the forum, according to time stamp, at 08:09 a.m. British time on June 28 -- about 17 hours before the bomb was found early on June 29.
Al Hesbah is frequently used by international Sunni militant groups, including al Qaeda and the Taliban, to post propaganda videos and messages in their fight against the West.
There was no way for CBS News to independently confirm any connection between the posting made Thursday night and the car bomb found Friday.
Al-Hazeen's message begins: "In the name of God, the most compassionate, the most merciful. Is Britain Longing for al Qaeda's bombings?"
Al-Hazeen decries the recent knighthood of controversial author Salman Rushdie as a blow felt by all British Muslims. "This 'honoring' came at a crucial time, a time when the whole nation is reeling from the crusaders attacks on all Muslim lands," he said, in an apparent reference to the British role in Iraq.
"We say to Britain: The Emir of al Qaeda, Sheikh Osama, has once threatened you, and he carried out his threats. Today I say: Rejoice, by Allah, London shall be bombed," the message reads.
Speaking at a news conference Friday after the bomb scare in central London, the Metropolitan Police force's Counter-Terrorism Commander Peter Clarke said that officials had "no indication that we were going to be attacked this way".
Prior to the Thursday night posting by al-Hazeen, there had been no specific allusions to threats against London or Britain seen on al Hesbah, or any other major jihadist forums in recent weeks.
Several responses to the posting by other forum members expressed hope that an attack against London would be realized in the near future.
In response, al-Hazeen urges patience, saying, "Victory is very close, but you are just rushing it."
Reached by CBSNews.com Friday, the Metropolitan Police's media office could not confirm whether investigators were aware of the Internet posting on al Hesbah.
Intelligence sources who spoke to CBS News Friday morning seemed to express surprise at the discovery of the device, suggesting there had been "no warning, no intel, no smell" as a prelude to the plot - a vacuum of information which reportedly had Britain's domestic intelligence agency "very, very worried".
The attempted bombing in London's Haymarket area came one week before the second anniversary of the July 7 bombings that killed 52 people on London's transportation network.
Also Friday, a London jury was expected to hand down a verdict in the case against five young men who were charged with trying to blow up city buses and trains in 2005.
The men, all from London, were arrested after police found homemade devices on trains and buses that had failed to detonate properly - sending puffs of smoke from backpacks that frightened commuters, but injured no one.
Early reports from law enforcement officials indicate that the car bomb found Friday morning may also have failed to detonate properly - causing smoke to appear in the passenger area. It was the smoke that prompted people to call explosives officers to the scene.
One explosives expert told the British Broadcasting Corporation that the device - comprised of gas canisters and nails - appeared to be a fairly crude construction, and not the work of anyone with an extensive knowledge of weaponry.
Britain has wrestled since the July 7, 2005, over how to deal with the threat of "homegrown" terrorism. Young men from the country's large Muslim population are easy prey for radical clerics and propaganda campaigns propagated on Internet forums such as al Hesbah.
In addition to messages calling for jihad in Britain, detailed video demonstrations of how to construct bombs using gas canisters are readily available on the forums.
By Tucker Reals