The FIR of the incident was filed at Shaheed Jamil police station, Quetta on June 6, it has emerged.
In his plea, Ahmed maintained that his father had filed a petition against the former premier under Article 6 of the Constitution, and went on to add that he was "certain" about his involvement in the murder.
The SC lawyer was fired upon by unidentified assailants on Quetta's Airport Road when he was on his way to Balochistan High Court (BHC), according to police.
He was rushed to Quetta Civil Hospital but he succumbed to his injuries while on the way to the medical facility.
Police surgeon Ayesha Faiz was quoted as saying at the time that Shar sustained 16 bullets in the attack.
On Tuesday, Special Assistant to Prime Minister (SAPM) Ataullah Tarar termed PTI chairman Imran Khan "directly responsible" for the lawyer’s killing.
He had alleged that the PTI chief got the lawyer killed to protect himself from the treason case and he'll be nominated for the murder of the SC lawyer.
The PTI had rejected “baseless and futile allegations”, and demanded that a case instead be filed against Prime Minister Shehbaz Sharif and Interior Minister Rana Sanaullah for the murder.
In a Twitter post, the party asked the Supreme Court to take urgent notice of the incident and the ‘false allegations’ being made against the former premier.
Last month, a division bench of the BHC heard the plea, wherein the lawyer had sought Imran Khan's trial under Article 6 of the Constitution.
He had pleaded that the ex-premier violated the Constitution by asking President Arif Alvi to dissolve the National Assembly, and so he should be tried under Article 6.