Aziz was suspected of killing T2F director Sabeen Mahmud, as well as being involved in Safoora Goth bus attack
Police will now look for another witness to implicate the suspects
Police say Ghulam Abbas, Sabeen's part-time driver, was shot dead after an altercation with an unidentified man
Mahenaz Mahmud talks about the Sabeen Mahmud Foundation, her plans to make T2F an independent project