Possibly another slant?

[budbondietti]

No: HPFGUIDX 139270

Having read a lot of the comments, I'd like to add my two cents worth. 
I do believe that Snape AK'ed DD but it was not for the completion of 
Draco's task or the UV. I believe that Snape fulfilled his committment 
to Narcissa when he healed Draco after the sectumsempra curse was 
performed by Harry. 

I believe that Draco's assignment from the DL was to create a means to 
get his DE's into Hogwarts for a confrontation with DD to stop his 
efforts to find the Horcruxes which he found out how DD was 
progressing by using Harry's vision. I find it hard to believe that 
the DL would not utilize any means of succeeding after all of the past 
failures. I also have a problem believing that the DL would assign 
such a gigantic assignment (doing in DD) to an unproven teen. 
Completion of the path from B&B to Hogwarts would be a start to prove 
Draco's worth and avenge his fathers incarceration.

These are my thoughts.

Bud