WASHINGTON — The three packages contained papers, books and other materials headed for Chicago. But officials now believe the September shipments were a dry run for the Yemen-to-Chicago mail bomb plot uncovered last week.
Before the packages reached their destinations, U.S. authorities seized and searched the boxes. They now appear to have been sent by the Yemeni militant group al-Qaida in the Arabian Peninsula to test the logistics of the air cargo system, a U.S. official said.
"We received information several weeks ago that potentially connected these packages to AQAP. The boxes were stopped in transit and searched. They contained papers, books and other materials, but no explosives," said the official, who was familiar with details of the shipments and spoke on condition of anonymity to discuss classified intelligence.
The official also disclosed that both mail bombs, one recovered in Dubai and the other in Britain on Friday, were wired to detonators that used cell phone technology. It still was not clear whether those detonators would have been set off by telephone calls or by an internal alarm.
The apparent dry run was first disclosed Monday night by ABC News.
The official said authorities, already aware of the militants' interest in striking at aviation, "obviously took notice" this past weekend and considered the likelihood that the militants might have extended their threat to the cargo system.
"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," the official said.
The threat last week came in the form of explosive devices hidden in the toner cartridges of computer printers. Investigators have centered on the Yemeni al-Qaida faction's top bomb maker, who had previously designed a bomb that failed to go off on a crowded U.S.-bound passenger jetliner last Christmas.
This time, authorities believe that master bomb maker Ibrahim al-Asiri packed four times as much explosives into the bombs hidden last week on flights from Yemen. The two bombs contained 300 and 400 grams of the industrial explosive PETN, according to a German security official, who briefed reporters Monday in Berlin on condition of anonymity in line with department guidelines.
By comparison, the bomb stuffed into a terrorist suspect's underwear on the Detroit-bound plane last Christmas contained about 80 grams.
"It shows that they are trying to again make different types of adaptations based on what we have put in place," said John Brennan, President Barack Obama's counterterrorism adviser. "So the underwear bomber, as well as these packages, are showing sort of new techniques on their part. They are very innovative and creative."
The U.S. and its allies Monday further tightened scrutiny of shipments from Yemen. U.S. counterterrorism officials warned police and emergency personnel to be on the watch for mail with characteristics that could mean dangerous substances are hidden inside.
Germany's aviation authority extended its ban on air cargo from Yemen to include passenger flights. Britain banned the import of larger printer cartridges by air on Monday as it also announced broader measures to halt air cargo from Yemen and Somalia.
A Yemeni government statement Tuesday expressed "sorrow and astonishment" at Germany's decision and said such a "rushed and exaggerated reaction to suspicious packages will harm Yemen's efforts in combating terrorism and serves no one but al-Qaida terrorists who always sought to ... hurt Yemen's interests, reputation and relations with regional and international friends and partners."
U.S. and British officials said they believed the targets were planes, not the two Chicago-area synagogues named on the addresses. Exactly how the bombs would have worked, however, remains a focus of investigators.