Actually the thing was covered in social media by journalists. Hamid Meer claims that such stuff could not be aired due to the fear more clashes will take place but it is pretty clear who is the culprit here:
Arshad Sharif @arsched12m
Horrifying reports of throats of madressah students being slit received during sectarian clash in #Rawalpindi . #Pakistan #Muharram
Arshad Sharif @arsched49m
Media teams beaten up in #sectarian clash in #Rawalpindi as authorities contact leaders of religious groups to control tempers #Pakistan
Arshad Sharif @arsched1h
Risk of sectarian clash high in #Rawalpindi as Commissioner recommends imposition of curfew. 7 dead. #Pakistan
Arshad Sharif @arsched1h
Situation critical in #Rawalpindi as students of madressah Taleemul Quran burned to death. 8 dead, 20 injured so far. #Pakistan
Arshad Sharif @arsched58m
Atleast 15 feared killed, 30 injured in #Rawalpindi sectarian clash as @CMShehbaz orders action against miscreants. #Pakistan
Mohammad Aftab @marimanj29m
@arsched @BushraGohar , private source tell 56 students killed by shia gangsters burned madina market stoped fire tenders to reach site.
Amer Khan @KhanAmerKhan6m
@arsched so far throats of 3 madressah students being slit during sectarian clash in Rawalpindi, situation is still critical
Khalid Khan™ @khalidkhan78730m
Update: At least 4 cameramen injured, 4 cameras, 1 DSNG damaged around Fawara Chowk, Rawalpindi, amid sectarian violence #Muharram #Ashura
Khalid Khan™ @khalidkhan7877m
update: Death toll in #Rawalpindi sectarian clashes rises to 11, over 35 injured, Madina Cloth market completely burnt #Muharram #Ashura
Khalid Khan™ @khalidkhan78712m
Just in: Rawalpindi administration decides to EXTEND #MobileJam (cell phone service ban) due to ongoing sectarian strife #Ashura
In any case, the mosque administrators have complained that media was not showing the dead bodies of students scattered in the seminary and took photos/ videos of the event itself. Thing will be out in a day or two.
The excuse that Matmi jaloos was incited by some mullah is ridiculous, its exactly the same thing Sunni extremist claim (with ref to first 3 claiphs and bibi Ayesha) it does not work for them and it won't work for Shi'ites.
Now that is much more pertinent than some sectarian rant. It seems that the armed(for their ritual) Shia group took advantage of their sharp tools. Old enmity with Madressa or genuine payback attack?