Rangers soldiers Shahid Zafar and Mohammed Afzal were handed over to police in Karachi on Friday by their military commanders, senior police official Tariq Dharejo told AFP.
"We have produced them in a session court where the judge remanded them into police custody for five days until Wednesday," Dharejo added.
Officials had said that five paramilitary soldiers were being held in connection with the killing in a park named after assassinated former Prime Minister Benazir Bhutto in the upmarket district of Clifton.
Dharejo said Zafar and Afzal were "the main accused" in the shooting, which was captured live on camera and broadcast repeatedly on local television and uploaded to an Internet video-sharing site.
Sarfaraz Shah, 22, was accused of robbery, but his family insisted he was an innocent student passing the time of day and has demanded justice.
Prime Minister Yousuf Raza Gilani said the culprits would be "prosecuted" and Major General Aijaz Chaudhry, the Rangers chief in the southern province of Sindh, said that a three-member team had been set up to conduct an inquiry.
"The incident is deplorable. The Rangers have no authority to kill any unarmed individual and they can fire only in self-defence," he said.
Leading human rights activists and lawyers condemned the killing as a sign of how brutalised Pakistan has become after years of bomb attacks, targeted assassinations, kidnappings and a Taliban insurgency in the northwest.
The incident mirrored the killings last month of five unarmed Chechens, one of them a pregnant woman, in south-western province Balochistan that is also under investigation.
Copyright AFP (Agence France-Presse), 2011