Investigators on Friday were still trying to determine whether three suicide car bomb attacks Thursday targeting Red Sea resorts in Egypt, filled with Israeli tourists, were carried out by al-Qaida terrorists. But an NBC analysis of the confluence of statements by Osama bin Laden's top lieutenant, Ayman al Zawahri, and terrorist attacks shows that on eight separate occasions, an attack attributed to al-Qaida quickly followed a statement by Zawahri.
Thursday's series of bombings followed by one week the last audio statement by Zawahri and by four weeks the last Zawahri video statement.
In four cases, the statement preceded the attack within a week, including a statement made last Friday that came only six days before the attacks on the Egyptian hotels in the Sinai. The statements that preceded attacks also represent the overwhelming majority of statements Zawahri has made in the past decade.
U.S. intelligence officials cannot say with certainty that the statements are "go signals," but they admit that they review the most recent statements after each al-Qaida attack. Thursday's attacks were no exception, said one U.S. intelligence official.
"I can’t get into that," said one U.S. official when asked if the intelligence community considered the tapes "go signals." "But I can say that not all of them are considered go signals."
U.S. officials have admitted that a Zawahri statement just before the Christmas holidays last year was a major reason for a Department of Homeland Security decision to raise the U.S. terror threat level from "yellow" to "orange."
Thursday's attacks followed by one week the last Zawahri audio statement and by four weeks the last Zawahri video statement. The audio statement appeared to be particularly relevant because he spoke of how "defending Palestine is the duty of all Muslims" and that all individual Muslims "must face the Jews" because their governments have failed the Palestinian cause.
On seven other occasions, a Zawahri statement preceded an attack. The interval between the statement and the attack varied from one day to 10 weeks. The longest interval, however, was between a statement calling on Muslims in Pakistan to kill President Pervez Musharraf and the first of two assassination attempts on him.
Here are the seven previous incidents where the attacks quickly followed a statement:
Aug. 6, 1998:
Zawahri sends a statement to a London-based Arabic newspaper saying, "We are interested in briefly telling the Americans that their messages have been received and that the response, which we hope they will read carefully, is being readied."
One day later, al-Qaida sent suicide bombers into the U.S. embassies in Nairobi, Kenya, and Dar Es Salaam, Tanzania. Truck bombs killed more than 240 people, including 12 Americans at the Nairobi embassy.
Sept. 21, 2000:
At the end of a videotape, Zawahri warns: "Enough of words. It is time to take action against the iniquitous and faithless force which has spread troops through Egypt, Yemen and Saudi Arabia."
Three weeks later, on Oct. 12, a bomb on board a small Zodiac-like boat detonates near the USS Cole in the port of Aden in Yemen, killing 17 U.S. sailors and wounding scores more. The bombing also kills two al-Qaida operatives in the boat.
April 17, 2002:
Zawahri and bin Laden praise the Sept. 11 bombers in a videotape recorded earlier, note the damage to the U.S. economy and call for more attacks.
Three weeks later, on May 8, 2002, A suspected suicide bomber in a car kills himself near a bus carrying 11 French navy experts and three Pakistanis outside the Sheraton Hotel in the southern Pakistani city of Karachi.
Oct. 9, 2002:
A Zawahri tape threatens attacks on the United States, its economy and allies. "I promise you that the Islamic youth are preparing for you what will fill your hearts with horror...."
Three days later, on Oct. 12, bombs explode in the Kuta Beach nightclub district of Bali in Indonesia, killing 202 people and wounding hundreds. Five Americans are among the dead. A third bomb explodes near the U.S. Consulate in Sanur near Kuta, without causing casualties. Bombers later admit they expected many more American casualties. The bombing highlights the reach of al-Qaida.
May 23, 2003:
A Zawahri audiotape aired on various radio and television outlets in the Middle East tells Muslims to "burn the ground under their feet, as they should not enjoy your protection.... Expel those criminals out of your country." And he condemns Saudi and other Arab governments. It concludes, "The coming days will bring to you news that will heal your hearts."
Two weeks later, on June 7, a suicide car bomber blows up a bus full of German peacekeepers, killing four and wounding 31 east of Kabul. An Afghan civilian and the bomber are also killed.
Sept. 29, 2003:
In an audiotape played on Al Jazeera and Al-Arabiya television, Zawahri called Pakistani President Musharraf a "traitor" for helping U.S.-led forces topple the Taliban regime in Afghanistan, for considering sending troops to Iraq and for considering recognizing Israel. "Muslims in Pakistan must unite and cooperate to topple this traitor and install a sincere leadership that would defend Islam and Muslims," said Zawahri.
Ten weeks later, on Dec. 14, Musharraf barely escapes death as his presidential motorcade travels over a bridge in Rawalpindi. The president is saved because of a jamming device on his car that scrambles signals on frequencies used to detonate remotely controlled bombs. The bomb detonates 30 seconds after the motorcade passes by. It is estimated to have weighed 1,000 pounds.
Dec. 19, 2003:
In a message delivered via al Jazeera television, Zawahri commemorates the second anniversary of the Battle of Tora Bora in Afghanistan with a cry for more attacks on Americans, including in the American "homeland." The Egyptian deputy to bin Laden claims the United States is losing the war on terrorism in both Iraq and Afghanistan, adding the U.S. "collapse" has started to become a reality and that the Americans have become "fugitives" in "Afghanistan, Iraq, Palestine and the Arabian Peninsula."
Two days later, on Dec. 21, U.S. intelligence fears the message could be a "go" signal for a terrorist attack and it becomes one of the reasons for the rise in the terror alert status two days later.
Then, on Dec. 25, six days after the statement, Musharraf survives a second assassination attempt on his life in Pakistan, this time when a suicide car bomber tries to ram the presidential limousine.
NBC's Robert Windrem is an investigative producer; Rob Rivas is a researcher for Nightly News.