Pakistani police have questioned more than 200 suspects in order to determine if the Muslim rampage that left eight Christians dead was premeditated.
A mob attacked and burned the homes of Christians in the city of Gojra on Saturday after allegations of a Koran being desecrated.
Officers arrested some people who allegedly belong to a banned Sunni group Sipah-e-Sahaba Pakistan and its al-Qaeda-linked offshoot Lashkar-e-Jhangvi.
Pakistani intelligence said Islamic militants were switching their tactics from suicide bombings to causing sectarian strife in the cities.
"We need to locate and arrest those who were wearing masks during the carnage," Punjab province Law Minister Rana Sanaullah told the Associated Press, referring to the attackers who were covering their faces during the rioting to avoid being identified.
Christian schools across Pakistan are closed for the next three days to mourn the deaths of their brethren.
*Original broadcast date: August 4, 2009.