Fearing a possible coded signal to attack, U.S. intelligence and law enforcement officials are studying an unusual pattern of words in the latest audiotape from al Qaeda’s No. 2 man, Ayman al Zawahri. On the tape, posted on the Internet Wednesday, Zawahri repeats one phrase three times at the end of his message. Have I not conveyed? Oh God be my witness. Have I not conveyed? Oh God be my witness. Have I not conveyed? Oh God be my witness. A new FBI analysis of al Qaeda messages, obtained by the Blotter on ABCNews.com, warns that "continued messages that convey their strategic intent to strike the U.S. homeland and U.S. interests worldwide should not be discounted as merely deceptive noise." THE BLOTTER RECOMMENDS Blotter Al Qaeda Leader on the Web Again — Instant Messaging Next? Blotter Al Qaeda No. 2 Makes More Threats Against the U.K. Blotter New Video From al Qaeda No. 2 Click Here to Check Out Brian Ross Investigative Photos Intelligence analysts are also investigating technical clues that Zawahri’s most recent audio message was phoned in via computer phone, using voice over Internet Protocol, or VoIP. The ease and frequency of Zawahri’s propaganda messages is one of the factors that have led U.S. intelligence analysts to worry about a possible attack against the United States this summer. The new FBI analysis, reviewing more than 70 al Qaeda messages over the last 14 years, found a recurring theme of "the duty to kill Americans — both military and civilian." Do you have a tip for Brian Ross and the Investigative Team?