The execution of Mumtaz Qadri on February 29 was described by analysts as a "key moment" in Pakistan's long battle against religious extremism, but it has also exposed deep religious divisions in the conservative Muslim country of 200 million.
An estimated 25,000 supporters of the former police bodyguard gathered in Islamabad's twin city Rawalpindi in the afternoon to offer prayers, before turning toward the heavily-barricaded capital which was patrolled by hundreds of police and paramilitary soldiers.
The protest has been almost entirely ignored by the Pakistani media, which has increasingly become subject to government-ordered news blackouts designed to prevent unrest from spiralling out of control.
Qadri was working as a bodyguard for Punjab governor Salmaan Taseer when he shot him 29 times in 2011 over the governor's call to reform the blasphemy law, which critics say is frequently misused to oppress religious minorities.
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Yesterday a group of angry men at a Pakistani airport assaulted a former pop star accused of insulting the Prophet Mohammed's youngest wife, in the latest case of vigilante violence linked to blasphemy.
The incident was captured on mobile phone video and has ben widely viewed.
The men, some wearing Western clothes and others in traditional shalwar kameez, were seen throwing punches at the 51-year-old, who in addition to his preaching work runs a chain of high-end clothing boutiques.
"You have committed blasphemy, hit him, hit him!" shouted one of the men.
"We were looking for you," said another. "He has disrespected the companions of Prophet Mohammed. He has blasphemed against the Prophet."
A local police official confirmed the incident and said the ex-singer had filed a complaint.
Most Internet users condemned the violence on social media.
"Get hold of the culprits and make an example of them. Enough of this madness in the name of love," wrote Facebook user Karami Elahi.