Why didn't Vladek kill Kluba and Pyra?

I'm gonna be very frank: Robal was real trash from the very start (and certainly before), therefore he deserved to die.

But why did Vladek spare Kluba and Pyra? Kluba was a real bastard and even killed Vladek's father. Vladek knew that from Romek.

As for Pyra, while he wasn't as bad as Robal and Kluba, he was a trashy kid too and he often helped Robal in his crimes.

«I was on the fire escape! I saw ya!»