The last call made by Shahzad that is reflected in the log was on May 12, seventeen days before his abduction on May 29, according to data obtained by The Express Tribune newspaper.
Hamza Ameer, the brother-in-law of the slain journalist, said he had found Shahzad`s mobile phone switched off when he tried to contact him at 5:42 pm on May 29.
Shahzad made his last call, according to the data, on May 12 near a cell phone tower installed atop a bank in Islamabad`s Blue Area.
Shahzad, according to the cellular phone data, was in Islamabad between May 1 and May 12.
A close friend of Shahzad told PTI that he had been able to call the slain journalist`s mobile phone early on May 30 but the call was disconnected after several rings.
Shahzad, who worked for Hong Kong-based Asia Times Online and Italian news agency Adnkronos International, was abducted shortly after he alleged in an article that al Qaeda had infiltrated the Pakistan Navy.
Journalists` groups and rights organisations have said they suspect Shahzad was picked up by intelligence operatives but the Inter-Services Intelligence has denied it was in any way involved in his kidnapping and murder.
Hamza Ameer said police were yet to register a "proper case" for the abduction and murder of Shahzad.
He said he filed a complaint after Shahzad went missing on May 30.
Later, the Margalla police station converted the complaint into an FIR without applying the law for abduction-cum-murder, Ameer said.
Another FIR was registered at Mandi Bahauddin in Punjab, where Shahzad`s body was found in a canal, and his autopsy was conducted in the district headquarters hospital in the town on May 30.
The Punjab police chief has issued a notification for setting up a three-member committee headed by a DIG to probe the killing.