CHICAGO - Attorneys for a Chicago businessman of Pakistani origin accused in the deadly 2008 Mumbai attacks on Tuesday painted the government's chief witness as a serial liar who struck a plea deal to save his life.

The witness, David Coleman Headley, whose late mother was a Philadelphia socialite and tavern owner and his late father a Pakistani official, has pleaded guilty to laying the groundwork for the three-day rampage in India's commercial capital.

He spent five days on the witness stand detailing how he received orders from a Pakistani extremist group and the country's main intelligence agency to conduct video surveillance in Mumbai.

But on Tuesday, attorneys for the businessman, Tahawwur Rana, told jurors that Headley's account was unreliable even though he is the government's key witness.

They said he lied to the FBI, a judge, and even one of his wives, and implicated Rana, his friend from school, in the plot because he was motivated by the plea deal - something he learned as an informant for the U.S. Drug Enforcement Administration.

"You knew if you don't get someone else arrested, all the weight of the case would rest on you alone?" defense attorney Patrick Blegen asked.

"Yes," Headley answered.

Rana has pleaded not guilty to charges he provided Headley cover as a representative of his immigration business to enable him to conduct surveillance for the Mumbai attacks, in which more than 160 people were killed.

Headley, who pleaded guilty to avoid the death penalty and extradition to India, wrapped up testimony Tuesday. Prosecutors said they expect to call up to eight more witnesses starting Wednesday.

Headley testified earlier that an extremist leader with ties to al-Qaeda - who is also charged in Rana's case - had plotted to attack U.S. defense contractor Lockheed Martin.

He told jurors that in August 2009 he used one of Rana's computers at his Chicago-based immigration-services business to begin researching Lockheed Martin for Ilyas Kashmiri, a Pakistani extremist leader, now at large, who was angry over the U.S. drone attacks inside Pakistan and wanted to target the defense contractor.

Headley did not provide details of the plot, which was not carried out. He said Rana did not know about it.