American intelligence officials had intercepted suspicious parcels containing books, papers and compact discs from Yemen to Chicago in September, and they now suspect those packages could have been a dry run for planning the route for the mail bombs last week.
In September, after receiving information linking the packages to Al Qaeda in the Arabian Peninsula, intelligence officers stopped the shipments in transit and searched them.
However, no explosives were found in those packages and they were allowed to continue to "random addresses" in Chicago, a New York Times report said citing two US officials speaking on conditions of anonymity.
"At the time, people obviously took notice and -- knowing of the terrorist group's interest in aviation -- considered the possibility that AQAP might be exploring the logistics of the cargo system," one of the officials said.
"The apparent test-run might have permitted the plotters to estimate when cargo planes carrying the doctored toner cartridges would be over Chicago or another city," The Times said.
"That would conceivably enable them to set timers on the two devices to set off explosions where they would cause the greatest damage".
One of the officials said that the Saudis tipped off the Americans last week that bombs may be sent from Yemen, which led to the prompt response.
The plot began to unravel after local authorities in the United Arab Emirates found a suspicious package from Yemen at the FedEx facility in Dubai on Thursday.
A routine security check at East Midlands Airport in central England found a toner cartridge that turned out to be a bomb on Friday afternoon.
The hunt is now on for Ibrahim Hassan al-Asiri, 28, a Saudi who is believed to be the top technical expert of Al Qaeda in the Arabian Peninsula, the Times said.
The intelligence officials suspect al-Asiri of designing the explosives that the underwear bomber planned to use on Christmas Day last year on a Detroit-bound airliner.
He is also believed to have crafted the body-cavity bomb that killed his younger brother, Abdullah al-Asiri, in a failed attempt to kill the top Saudi counterterrorism official, Prince Mohammed bin Nayef.
Meanwhile, the 22-year-old female engineering student arrested by Yemeni authorities, in connection with the two mail bombs was released on Sunday with no charges.
The authorities had tracked her down from the name and phone number on the shipping documents but the woman's identity appears to have been stolen by another woman who dropped off the package.
