According to Pakistani media, the investigators could not get any lead linking the attackers with any group outside the jail.
One of the attackers told the investigators that they had planned Sarabjit's killing at their own to stop his possible departure to India, saying that Singh was a terrorist and responsible for bomb blasts in Pakistan.
But since the Pakistani prisoners are from street-gangs in Lahore's Islampura neighbourhood and hardened criminals, this 'noble' intention is a suspect.
The more possible reason could be that they want to delay their death sentence and Sarabjit's killing serves in two ways. One, by killing an Indian they become darlings of Pakistani militants and secondly, the fresh case will delay their execution in previous case.
One of the investigator said "It looks like they attempted another murder to delay the death sentences awarded to them."
The investigators on Saturday visited the crime scene, collected evidences and recorded the statements of the witnesses.
Meanwhile, an intelligence official discarded any conspiracy theory behind the attack.
Singh was attacked by two fellow inmates - Amir Tanba and Mudasir - in Lahore's Kot Lakhpat jail on Friday afternoon when he was outside his cell for a routine walk along with other inmates also sentenced to death. Two armed jail wardens - Adnan and Safdar - were also present at the spot and tried to stop the attackers. Neither of them could protect him and were themselves injured in the process.
The attack was pre-planned. Singh's lawyer, Awais Shaikh, told Dawn.com he had written a number of letters to the prison authorities, as well as high-level government officials on the complaint of his client that certain inmates were threatening him and his life was in danger. Shaikh added that these requests were not heeded, and further went on to allege that the jail authorities were themselves involved in the brutality.