Testimonies of witnesses produced by the CBI, which investigated the case, were not reliable, as some of them were accused-turned-prosecution witnesses, he said.
Satish Verma, a Gujarat-cadre IPS officer, who assisted the CBI in the investigation, "tampered with the evidence," Amin alleged.
The agency had said in the chargesheet that Amin fired five rounds at Ishrat and four others during the alleged fake encounter.
Amin also sought relief on the ground of parity, as former in-charge DGP of Gujarat P P Pandey, a former accused in the case, has been granted discharge by the court.
The CBI lawyer maintained that it had sufficient evidence against Amin as well as retired IPS officer D G Vanzara, another accused whose discharge plea is pending.
Amin, who retired in August 2016, was given extension by the state government. He was later forced to resign on the direction of the Supreme Court after a petition challenged his and co-accused Tarun Barot's re-induction into the force.
The court will hear Vanzara's discharge plea on June 5.
Ishrat, a 19-year-old college girl from Mumbra near Mumbai, her friend Javed Sheikh alias Pranesh, Amzad Ali Rana and Zeeshan Johar were killed in an alleged fake encounter by the Ahmedabad police on the outskirts of the city in June 2004.
The police had claimed that they were terrorists affiliated to the Pakistan-based Lashkar-e-Taiba.
While Pandey was discharged, all others are out on bail.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)