ISI stands for Inter-Services Intelligence. An array of American officials says bin Laden was sheltered by current and former Pakistani spy agency employees.
Beginning Monday at the Dirsken Federal Building, a terrorism trial starts that might as well be entitled ISI Chicago with Pakistan's spy agency front and center.
Since the moment Navy Seals took down al-Qaida founder Osama bin Laden, Pakistan has tried to deflect accusations that its spy service ISI and its army were secretly helping bin Laden.
But next week begins a federal trial here in Chicago, where federal prosecutors will state openly that some working for ISI were involved in international terrorism. It is the case of Tahawwur Hussein Rana, a 50-year-old Pakistani-born Chicagoan who operated a North Side travel agency and immigration aid service. Rana is charged with helping to plot the 2008 massacre of more than 160 people in Mumbai, India. He was originally arrested with Chicagoan David Coleman Headley who has since pleaded guilty and will be the prime witness against Rana.
"Part of the defense will be that Headley used his connections with ISI to explain the things he was doing," said Patrick Blegen, Rana's attorney.
Headley, a Pakistani-American businessman-turned-militant, is expected to testify that he trained fives times at terrorist camps in Pakistan and was then recruited by ISI officers to plan and prepare for the 2008 attack on India's largest city.
Headley, whose plea bargain allows him to avoid the death penalty, will also implicate Rana as a terrorist messenger and co-planner, something Rana strongly denies.
"We are very much looking forward to cross examination of Mr. Headley," said Blegen.
Rana's relatives in Chicago have appeared in overseas interviews defending him. And well before bin Laden was killed, the Chicago case has attracted significant attention on India TV.
Late last month, federal prosecutors in Chicago quietly added several new defendants to the terrorism case. One was an ISI major at the time of the Mumbai massacre. All had connections to the ISI or to Pakistan' military.
"The ISI had knowledge of these attacks in Mumbai before they happened," said Kim Barker, journalist and author.
Barker works for a non-profit investigative news agency. She wrote a book on the taliban after covering Pakistan for five years as a Chicago Tribune foreign correspondent reporting on the Pakistani intelligence service.
"As a journalist who lived there more than 5 years, we were always aware the ISI was monitoring everything we were doing....for some of these people, there ties are so tight with militants that they feel more allied with them than with the leadership of the ISI," said Parker.
For more than 10 years U.S. diplomats and military officials have charted ISI's relationship with al-Qaida; the spy agency ignored growing ties between Osama bin Laden and the Taliban.
In an exclusive ABC interview this week, even Pakistan's former president said ISI agents were to blame for bin laden living under their noses.
"It's really appalling that he was there and nobody knew...people must be punished," said Pervez Musharraf, former president of Pakistan.
Could it be that Musharraf himself gave bin Laden safe haven in Pakistan? That question is being raised a retired lieutenant general in the Pakistani military who suggests Musharraf might have been waiting for the appropriate moment to announce bin Laden's capture. The U.S. has demanded the names of ISI operatives to investigate what dealings they may have had with al-Qaida.