By Syed Shoaib Hasan
BBC News, Karachi
Karachi police were told to patrol unarmed on Saturday despite widespread predictions that rival demonstrations would degenerate into violence.
A number of people were injured in clashes
At least 41 people died in some of Pakistan's worst political violence in recent years.
Armed groups of political activists clashed for two days. Police have been accused of standing by.
Opposition parties had been planning a mass rally in support of the suspended chief justice of the Supreme Court.
Iftikhar Chaudhry was unceremoniously suspended by President Pervez Musharraf on 9 March.
Gen Musharraf accused him of misuse of office. The judge's supporters say the president was trying to stifle the independence of the judiciary in an election year.
The country has since seen widespread anti-government protests by lawyers bodies and opposition parties.
Mr Chaudhry was planning to address a rally of supporters in central Karachi on Saturday.
Then the MQM, the ruling party in Sindh province, said it would hold a pro-government rally on the same day.
Mr Chaudhry was suspended from his post in March
Subsequently, senior government figures and analysts expressed fears that there could be serious violence in Karachi.
The city authorities said that they had taken all possible measures to prevent any trouble.
However, according to documents obtained by the BBC, these measures included the instruction that "no police personnel should carry any kind of weapon during the law and order duty with the rally".
The directives were part of a security plan issued by the office of the police chief of Karachi, Azhar Faruqi.
The documents warn of the possibility of "suicide attacks" as well as "clashes between rival political parties".
Almost all the people killed were shot dead during armed clashes between groups of MQM and Pakistan People's Party (PPP) supporters.
Of all the police officials were deployed for security duties in Karachi, only 21 were armed.
Analysts say that the way police were deployed indicates that they were meant to stop people gaining access to the airport or to the High Court.
As the violence worsened, Chief Justice Chaudhry decided not to leave the airport and abandoned plans to address his supporters.
On Saturday police chief Azhar Faruqi was summoned by High Court and ordered to take action to stop the mayhem.
He answered that "he was helpless to do anything".
Later, Sindh province's de facto home minister, Wasim Akhtar, told a local television channel that the police and other law-enforcing agencies were told not to fire back as it would have increased tension and led to more casualties.