One visit was to an Islamic foundation in a northern suburb, which had recently received a Fedex letter from Yemen, but told nobody about it. About the same time, federal authorities say the bomb plotters had attempted a dry run of the attack, which ultimately used the former addresses of two Chicago synagogues.
A few weeks earlier, al-Qaida's online magazine had published a photograph of Chicago's skyline, with the nation's tallest building, the Willis Tower, front and center.
Investigators trying to unravel the mail bomb plot say the terrorists never expected the explosives to be delivered to the old Chicago addresses, but questions remain about what role the city plays in the international who-done-it.
The packages were found last month on planes in Britain and in Dubai before the bombs ever went off, but U.S. officials say evidence suggests al-Qaida's aim was to blow up planes inside the U.S., either on runways or over American cities. Whether they had targeted Chicago specifically isn't known.
So little information has come out about the investigation that U.S. Reps. Jesse Jackson Jr. and Jan Schakowsky on Monday called for congressional hearings.
"A public hearing would bring clarity to these questions on behalf of the people of Chicago and the country," wrote Jackson and Schakowsky, both from Illinois, in a letter to the Committee on Homeland Security.
Authorities are still trying to figure out why the addresses on the packages were for buildings no longer used by Jewish synagogues — one of buildings is now empty and other is a Unitarian church that had stopped renting space to a Jewish congregation seven years ago.
Even stranger: the names on the packages were not for people in Chicago but rather obscure historical figures. One packages was addressed to Diego Deza, a figure from the Spanish Inquisition, and the other for Reynald Krak, who was beheaded by a Muslim general during the 12th century Crusades.
The FBI and local authorities are not saying much publicly about whether al-Qaida has specifically targeted Chicago or if the Chicago mentions are a coincidence. About the only thing agents said when they visited the IQRA International Educational Foundation is that they knew about the letter the Skokie, Ill.-based nonprofit Islamic foundation received from Yemen.
"They said anything emanating from that area, they were tracking it," said IQRA's financial manager, Wahaj Ahmed, who said the agents never hinted that the foundation did anything wrong. "Anything that was sent from that place or sent to that place (Yemen), that's how they came to know about this particular letter."
Terrorism experts say when it comes to al-Qaida, nothing just happens. Everything is planned.
"I don't dismiss anything as a coincidence," said Sam Kharoba, founder of the Florida-based Counter Terrorism Operations Center, and who trains law enforcement agencies on counterterrorism. "These guys (al-Qaida) are professionals."
Kharoba said radical Muslims are paying attention to what al-Qaida's online magazine called "Inspire" has to say, and that has him worried about the photograph.
"Historically they go after iconic targets," Kharoba said. "The Sears Tower (now the Willis Tower) is one of those."
Even if the bombs didn't reach Chicago, the message did, said Michael Kotzin of the Jewish United Fund/Jewish Federation of Metropolitan Chicago.
"Mailing them to (former) synagogues was deliberate," Kotzin said. "Jews are a priority target for them. That is what they are saying."
Other terrorism experts float various theories for why the plotters may have chosen Chicago.
"I think the primary interest in Chicago is that it is the power base of President (Barack) Obama," said Evan Kohlmann, a terrorism analyst with Flashpoint Global Partners, a New York-based security consultancy.
At the same time, blowing up a plane near or over Chicago would likely cause more collateral damage on the ground because, unlike New York or Los Angeles, the city is not near an ocean, he said.
It would not have been the first attempt to strike at the U.S. interior by al-Qaida in the Arabian Peninsula, the Yemen-based offshoot that claimed responsibility for the mail bomb plot.
Last Christmas, a Nigerian with links to al-Qaida in Yemen was subdued by passengers on a plane bound for Detroit as he tried to detonate explosives concealed in his underwear.
Still, there's some skepticism whether or not the plot means Chicago is at any more risk than other large U.S. cities.
"I'm not convinced that Chicago is necessarily a new target," said Paul Goldenberg, national director for the Secure Community Network, a homeland security group for American Jewish organizations that first informed Chicago's Jewish community of the plot. "At the end of the day it comes down to where do they (terrorists) have the greatest opportunity."