U.S. intelligence officials said Monday packages they seized in September may have been a "dry run" for the Yemen-to-Chicago mail bomb plot uncovered Friday.
Federal agents intercepted three suspicious packages in mid-September before they reached their Chicago destinations. They removed papers, books and other materials that may have been sent from Yemen by "someone with ties to al Qaeda in the Arabian Peninsula," ABC News reported.
"When we learned of last week's serious threat, we recalled the (September) incident and factored it in to our government's very prompt response," a U.S. official said.
According to another person briefed on the attack, officials believe the terrorists sent the packages sent the packages to "track how long it took and whether there would be any problems for the package getting through the system."
Ibrihim Asiri, the man who constructed the mail bombs, is also allegedly responsible for making the explosives used by his brother, the so-called underwear bomber, last Christmas.
The 28-year-old Saudi native is an expert in explosives and chemicals and a fanatical member of al Qaeda.
Meanwhile, Yemeni prosecutors have charged U.S.-born cleric Anwar al-Awlaki with plotting to kill foreigners and being a member of al Qaeda. Al-Awlaki is believed to be a co-conspirator in last year's failed Christmas Day bombing attempt.
The New York Daily News reported the charges by Yemen were the first formal legal action against the cleric.