The federal government’s key witness in the trial of a Chicago businessman accused in the 2008 Mumbai attacks testified Monday that he first started training more than a decade ago with a Pakistani militant group that received assistance from the country’s main intelligence agency.

The trial of businessman Tahawwur Rana is being closely watched worldwide for what testimony might reveal about suspected links between the Pakistani militant group blamed in the rampage on India’s largest city and Pakistan’s main intelligence agency, which has come under increased scrutiny since Osama bin Laden was killed by U.S. forces on May 2 outside Islamabad.

Of particular interest is the government’s first and main witness, David Coleman Headley, who is cooperating with prosecutors after pleading guilty to taking photos and videos of targets in Mumbai before the rampage that killed 160 people including six Americans over three days. Rana is accused of providing cover for Headley by allowing him to use his Chicago-based immigration services business as a cover when he traveled to India.

Headley, Rana’s long-time friend from boarding school, told jurors Monday that he received weapons and leadership training with the militant group Lashkar-e-Taiba since 2000 and it was his understanding that Lashkar and Pakistan’s Inter-Services Intelligence agency, known as the ISI, helped each other in general.

“They coordinated with each other and ISI provided assistance to Lashkar,” said Headley, who spoke in a soft voice and with a slight British accent. He did not immediately give any specifics.

Headley said that when Lashkar leaders began talking about a possible attack in India, he suggested that he get involved.

“I suggested that I change my name and make a new passport to make it easy to enter India undetected,” Headley testified.

Earlier Monday, attorneys painted dueling portraits of Rana, 50, who has pleaded not guilty.

Defense attorneys said their client was simply taken advantage of by his longtime friend and did not know what was in store. Headley and Rana, a Pakistani-born Canadian who has lived in Chicago for years, met at one of Pakistan’s most prestigious military boarding schools and stayed in touch as adults.

Defense attorney Charles Swift told jurors during opening statements that Headley, a Pakistani-American, was a “manipulative man” who “balanced multiple lives” including working for Laskhar-e-Taiba, Pakistani intelligence and the U.S. Drug Enforcement Administration at the same time.

“David Headley … has been manipulating people for years. Dr. Rana is by far and away not the first,” Swift said during opening statements.

But Assistant U.S. Attorney Sarah Streicker said Rana was not duped and knew of the plans. She said Rana provided cover for Headley and led him to pose as a representative for his Chicago-based immigration business. She also said Rana knew and supported a separate plot that never happened against a Danish newspaper that had printed cartoons of the Prophet Muhammad and that Rana and Headley had talked about at least four other plots. She gave no further details.

“The defendant knew all too well that when Headley travels to a foreign country, people may die,” Streicker told jurors.

Streicker said the government will show jurors evidence including emails between Headley and Rana that were written in code. She said Headley considered Rana “his best friend in the world.”

“The defendant didn’t carry a gun or throw a grenade. In a complicated and sophisticated plot, not every player carries a weapon. People like the defendant who provide support are just as critical to the success,” Streicker said.  

Attention to Rana’s trial has increased in recent weeks, especially amid questions about whether the ISI had knowledge of bin Laden’s whereabouts. Security has been tightened, with more armed guards and a metal detector outside the courtroom in downtown Chicago, and many reporters from Denmark and India are covering the proceedings.       

“The trial has the potential to be an irritant and already has been in what’s happening in the U.S.-Pakistani relationship,” said Daniel Markey, a fellow at the Council on Foreign Relations. “Given the Indian media attention, it’ll stoke Indian concern about what Pakistan has been up to.”

But some experts are doubtful the trial will reveal much new. For one, federal prosecutors may work hard to keep any sensitive information from surfacing in the courtroom, and Headley’s credibility has been under question.

Headley, born Daood Gilani, reached a plea deal with prosecutors in the terrorism case in exchange for avoiding the death penalty and avoiding extradition. He’s also been an informant for the DEA after a drug conviction.

Rana is the seventh name on the indictment, and the only defendant in custody. Among the six others charged in absentia is “Major Iqbal” and Sajid Mir, allegedly another Lashkar-e-Taiba supervisor who also “handled” Headley.