Book 6 prediction - Regulus Black

[Hagrid]

No: HPFGUIDX 81178

There are obvious personalities from the Death Eaters that are 
touching the emotions of Dumbledore's Army. (eg: Lestrange attacked 
Harry's godfather and Neville's parents)

My query is about another DE victom. Regulus Black, Sirius's younger 
brother. 

- Which witch or wizard killed Regulus?
- Was this done with the Dark Lord's approval?

If he wasn't killed on LV orders, then:-
... Regulus would have been a year or two behind Sirius in Hogwarts, 
and would have known his brother's friends and rivals ... that means 
either Peter Pettigrew killed Regulus, or Severus Snape did.