The CBI earlier interrogated Gujarat Chief Minister Narendra Modi's close aid and former state home minister Amit Shah in connection with the case.
The federal agency on Spet 23 quizzed Gujarat Law Minister Pradeep Singh Jadeja.
The CBI on Sept 20 questioned suspended Indian Police Service (IPS) officer DG Vanzara at the Sabarmati Jail here over his resignation letter in connection with the case.
Vanzara had said in his letter that officers like him were made to suffer in jail even after being "loyal" to the government and blamed Gujarat Chief Minister Narendra Modi for not helping these cops.
In a 10-page letter written on Sept 1 from prison, Vanzara, who has been suspended from service, said he was resigning from the police force.
"I along with my officers stood beside the state government like a bulwark whenever it faced existential crisis in the past. It was expected of the government to reciprocate and stand firmly with us with a similar vigour and determination which to my utter shock and surprise did not happen," he said in his letter.
The letter was sent to Home Ministry in Gujarat and the CBI.
Nineteen-year-old Ishrat was gunned down by the Gujarat Police along with Javed Ghulam Sheikh alias Pranesh Kumar Pillai, Amjad Ali alias Rajkumar Akbar Ali Rana and Jisan Johar Abdul Gani in Ahmedabad on June 15, 2004.
The police alleged that Ishrat and three others were Lashkar-e-Taiba (LeT) militants who conspired to assassinate Gujarat Chief Minister Narendra Modi.
--IBNS (Posted on 14-10-2013)