"The involvement of an insider in the police department who might be a Taliban sympathiser or activist is not being ruled out, nor is the involvement of family members or friends," said an official who did not want to be named.
Aslam was killed with two other policemen when a suicide bomber rammed an explosives-laden vehicle into his motorcade in Karachi on Thursday.
Besides the police, a special team of the Military Intelligence and Federal Investigation Agency is investigating the attack.
Another official said two members of Aslam's family were called in for questioning.
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Aslam always kept his movements secret as he was on the hit list of terrorists and criminal organisations.
In the past, sympathisers of the Taliban within the police department were arrested for selling out fellow officers and colleagues, an official said.
The Karachi police team led by DIG (CID) Zafar Bukhari, which is investigating the attack, claimed a seminary student named Naeemullah was the suicide bomber who targeted Aslam's convoy.
"The interesting thing is that Naeemullah's brother was reportedly killed some time back by the Taliban for failing to carry out a terrorist attack," one official said.
Evidence collected from the site of the blast has been sent to Islamabad for DNA tests to confirm Naeemullah's involvement in the attack.
After his slaying, police and paramilitary Pakistan Rangers launched operations in areas of Karachi where the Taliban and other militant groups have reportedly set up safe houses.