CHICAGO (AFP) - A Pakistani-based branch of Al-Qaeda was hatching a plot to kill the head of US defence group Lockheed Martin, self-confessed terrorist David Coleman Headley testified in a US court Tuesday. The planned assassination was in retaliation for the Lockheed Martin-made drones, Headley testified during the Chicago trial of his childhood friend, Tahawwur Hussain Rana. Headley pleaded guilty to 12 terrorism charges related to the deadly 2008 Mumbai attacks and other unrealised plots in the wake of his 2009 arrest in Chicago. He is testifying against alleged co-conspirator Rana in exchange for avoiding the death penalty and extradition to India, Pakistan or Denmark. Headley testified that he secretly used Ranas office computer for research on the plot to assassinate the Lockheed Martin executive but dismissed his brief online search there as insignificant.