The paramilitary troopers were deployed in the city on Thursday after enraged protesters attacked the offices of the ruling party's lawmakers over failure of police to make headway in the probe into the rape and murder of the 7-year-old girl. The girl was strangled to death after being raped. Her parents returned to the country on Wednesday, one day after the girl's body was found.
Zainab went missing January 4, as she was heading to a class at a religious school near her home.
According to CCTV footage, the girl in Kasur district was abducted last week outside her home.
However, Samaa TV's news anchor Kiran Naz chose a novel method to address the issue. During the show, she said, "Today I'm not your host Kiran Naz".
Zainab's mother, standing behind Ansari outside the airport, said: "I don't know anything".
Referring to Zainab, she said "the smallest coffins are the heaviest, and the entire society is burdened by the weight of her coffin".
Three police officers were arrested for opening fire on protesters instead of into the air.
A local police spokesman told AFP news agency "up to 1,000" people had taken to the streets.
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Violence broke out Wednesday when demonstrators tried to storm the police station, the police official said.
Up to 20 people have been arrested over Zainab's murder "but the investigators have been unable to find any clue so far" Mr Sajid said.
Zainab was kidnapped on her way to a Koran recital while her parents where in Mecca performing a religious pilgrimage.
Zainab's father Ameen called on the government to publicly punish the perpetrator.
Local politicians have met the family and promised the killer would be caught.
"Police are not cooperating with us", claimed Ghulam Rasool, an uncle of Zainab. We don't want an innocent to be presented as the culprit and killed just to wash this case'.
The Lahore High Court's Chief Justice, Punjab's Chief Minister, the Senate, the Chief Justice of Pakistan and the army chief have all spoken out on social media about the case.
The horrific incident triggered public outrage throughout the country with people demanding justice for the child.
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