It’s too early to blame it on any one particular group. City has a history of sectarian violence. Sippah-e-Sahaba, Sippah-e-Muhammad, Lashkar-e-jhangvi & Tehreek-e- jafriyah ect were involved in such activities, in past, when there was no sign of talibans in Pakistan.
Lets see if any group ownes the responsibility and what investigations reveals.