It seemed clear that the police did not just fire tear gas cannisters to disperse the crowd but had intention to punish participants, probably to discourage future participations.
Why would I say so? Because police fire tear gas cannisters in order to box in the fleeing crowd. Not only that, why else would they shut all the nearby LRT stations even around 5pm when people were trying to leave if not to trap them where they are?
Here is an account of a very elderly lady in the 70's:
"Stumbled our way to the back but met with more tear gas coming now from the Jalan Raja Laut area. Nowhere to run. How to disperse? Why were they trapping people by firing from front and back? Such confusion for everyone fleeing and not knowing where to run."
Source: Bersih 3.0: Malaysia at its best and worst